The Noise

01What's that sound?

The short version: Search everything in this guide by what you are hearing - "humming at night", "beeping crosswalk", "siren that rumbles", "jackhammer at 7am", "train horn", "birds singing at 3am" - and jump to the explanation. Below it, the decibel ruler puts the sounds in this guide on one scale, from rustling leaves to a jet engine, with the hearing and noise limits marked.

Every sound on one ruler

Each bar is a sound level reported by a source cited in this guide. Decibels are logarithmic: every 10 dB step is ten times the sound energy and sounds roughly twice as loud, so the bars near the top of the scale are far louder than they look. Levels depend heavily on distance and conditions, so tap a bar to see the measurement and its source.

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02Sound and decibels in plain words

The short version: Sound is a small, fast wobble in air pressure, and noise is sound somebody did not ask for. Loudness is measured in decibels, a logarithmic scale where two equal sources add up to only 3 dB more and it takes about 10 dB more for something to seem twice as loud. Every decibel number needs a label - dBA, dBC, Leq, Lmax, DNL, Lden - because each one measures something different, and comparing across them is how most noise arguments go wrong. Distance, walls and pitch then decide what actually reaches you: bass slips through walls that stop voices, and a highway carries much farther than a single horn.

What is sound, exactly?

What you hear: everything, from a bus pulling away to a fridge humming in the next room.

The FAA's plain definition is a good start: sound is "energy transferred through the air that our ears detect as small changes in air pressure."⁴ Noise is "sound that is unwanted," which gives it two sides: a physical one you can measure and a subjective one you cannot.⁴

The pressure changes involved are tiny. The quietest sound a healthy young ear can detect, the threshold of hearing, is a pressure change of about 20 micropascals, which is defined as 0 dB.⁵ The threshold of pain is put at about 140 dB, or 200 million micropascals, by the Federal Highway Administration,⁵ while the FAA puts the loudest sounds we hear without pain at about 120 dB and says most everyday sounds fall between 30 and 100 dB.⁶ The agencies differ on the top end, so "about 120-140 dB" is the honest range. That ten-million-to-one span in pressure is why decibels use a logarithmic scale.

How high and how low can people hear?

What you hear: pitch - the low rumble of a truck engine, the high whine of a scooter motor.

Frequency is how many pressure cycles pass per second, measured in hertz (Hz), and we hear it as pitch. Human hearing runs from about 20 Hz at the bottom to somewhere between 10,000 and 20,000 Hz at the top, according to the FAA.⁶ The top end falls with age and with hearing damage, which is why a teenager can hear a high-pitched hiss an adult cannot.

The ear is not equally sensitive across that range. The FAA describes peak sensitivity between about 500 and 2,000 Hz,⁶ and an acoustics vendor glossary gives a wider band of about 500 Hz to 6 kHz.⁷

Each frequency has a wavelength, the physical length of one cycle in the air. Wavelength is the speed of sound (about 343 m/s) divided by frequency, so a 20 Hz bass note is about 17 m (56 ft) long, 100 Hz about 3.4 m, 1 kHz about 34 cm and 4 kHz about 8.6 cm.⁸ A wave the length of a city bus behaves very differently from one the width of your hand, and that difference explains a lot of what follows.

Why don't decibels add up?

What you hear: a second leaf blower starts across the street, and the noise gets worse, but not twice as bad.

The decibel (dB) is "a logarithmic unit which expresses the ratio of the sound pressure level being measured to a standard reference level."⁹ Because it is a ratio on a log scale, decibels do not add like ordinary numbers.

Two identical sources together are 3 dB louder than one, because doubling the energy adds 3 dB. The FHWA's example: two 90 dB trucks make 93 dB, not 180 dB.⁹ For uneven sources, the FHWA offers a shortcut: if two levels are 0-1 dB apart, add 3 dB to the higher; 2-3 dB apart, add 2; 4-9 dB apart, add 1; 10 or more apart, add nothing.⁵ A loud source swamps a quiet one: the FHWA's 60, 60, 65 and 75 dB sources total about 75.7 dB.⁵

Perception follows a different rule from energy. A 10 dB increase is heard, on average, as a doubling of loudness, so 70 dB sounds about twice as loud as 60 dB.⁹ A 3 dB change is a "barely perceptible change" and a 5 dB change a "readily perceptible change."⁹ The FHWA calls a 20 dB(A) cut "one-fourth as loud."⁵ The "10 dB is twice as loud" rule is an average of how people judge loudness, not physics; in energy terms, 10 dB is ten times the energy.

What is the difference between dB, dBA, dBC and dBZ?

What you hear: a meter showing a much higher number in dBC than in dBA for the same thumping car stereo.

Meters filter the signal before reporting a number, a step called frequency weighting; the letter after "dB" names the filter.

A-weighting (dBA) mimics human hearing at moderate levels. It turns down frequencies below about 500 Hz and above about 10,000 Hz and is nearly flat in between, and it is the basic environmental noise measure used by EPA and most agencies.⁶

C-weighting (dBC) is much flatter and keeps more of the bass. It is "commonly used for the measurement of Peak Sound Pressure level."⁷ A bass-heavy source reads higher in dBC than in dBA, so a big gap between the two is a sign that most of the energy is low.

Z-weighting (dBZ) is "zero" weighting: "a flat and unadjusted frequency response between 10 Hz and 20kHz."⁷

Meters also apply a time weighting that controls how fast the display reacts: Fast is 125 milliseconds, Slow is 1 second, and Impulse (rarely used) is 35 milliseconds. A peak reading has no time constant at all - it catches the single highest instantaneous pressure.⁷

The rule for reading any noise number: 70 dBA and 70 dBC are different measurements of the same sound, and neither can be compared with the other. The free NIOSH phone app lets you switch among A, C and Z weighting.¹⁰ For how this plays out with concert systems, see The Show File's guide to concert sound.

Which number is the "real" level? Leq, Lmax, L10, L90 and SEL

What you hear: a quiet street, then a motorcycle, then quiet again. What was "the" level?

Leq (equivalent continuous level) is the energy average: "the level of continuous sound over a given time period that would deliver the same amount of energy" as the fluctuating sound.⁴ An A-weighted Leq is written LAeq. Many US state highway agencies use Leq(h), the hourly A-weighted Leq.⁹

Lmax is the loudest moment in the period. It ignores duration entirely: the FAA notes that a gunshot and a nearby freight train can share the same Lmax even though the train lasts far longer.⁴

L10 and L90 are statistical levels: the level exceeded 10% of the time and 90% of the time. L10 is common in traffic work; L90 is a standard measure of ambient or background sound.⁷ If a complaint is about a constant hum (see hums and drones), L90 tends to capture it. If it is about passing trucks, L10 and Lmax do.

SEL (sound exposure level) takes one event's total energy and expresses it "as if that event had occurred within a one-second period."⁴ For most aircraft overflights, SEL runs about 7-12 dB higher than the Lmax of the same event.⁶

What are DNL and Lden?

What you hear: an airport or rail report says your street is "DNL 62" or "Lden 58."

These are long-term, 24-hour averages with a penalty added for noise at night, when it bothers people more.

DNL (day-night average sound level, also written Ldn) is the US standard. It counts A-weighted sound between 10 p.m. and 7 a.m. as 10 dB louder than it really is.⁶ DNL is the standard metric for all FAA aviation noise studies.⁴ Because it is an energy average, many quiet events and a few loud ones can produce the same number: the FAA notes that DNL 65 results from 1 event a day at SEL 114.4 dBA, 10 events at SEL 104.4, or 100 events at SEL 94.4.⁴ Residents and airports can look at the same DNL and describe very different experiences; the aircraft section covers how that plays out around airports.

Lden (day-evening-night level) is the European version. By default the day runs 07:00-19:00 with no penalty, the evening 19:00-23:00 with +5 dB, and the night 23:00-07:00 with +10 dB; member states may shift the hours.¹¹ The EU's Environmental Noise Directive uses four indicators: Lday, Levening, Lnight (the night average on its own) and Lden.¹²

DNL and Lden are cousins, not twins: different hours and the evening penalty give the same sound different values, so do not read one as the other.

How much quieter is it twice as far away?

What you hear: a jackhammer fades fast as you walk away; the highway hum follows you for blocks.

It depends on the shape of the source. A point source - one horn, one jackhammer - spreads sound in a sphere, and the level drops about 6 dB(A) each time you double your distance: the FHWA's example goes from 90 dB(A) at 15 m (50 ft) to 84 dB(A) at 30 m (100 ft).⁵

A busy road behaves like a line source, a long stream of point sources that spreads as a cylinder. It drops only about 3 dB(A) per doubling: 90 dB(A) at 15 m becomes 87 dB(A) at 30 m.⁵ Over soft ground such as grass, the usual traffic analysis rate is 4.5 dBA per doubling,⁹ because soft ground absorbs about an extra 1.5 dB(A) per doubling; over hard ground, the FHWA reports levels 1-2 dBA higher for the first rows of homes near highways.⁵

So moving from 15 m to 60 m (four times the distance) cuts a single horn by about 12 dB but a highway by only about 6 dB over hard ground. The FHWA says traffic noise is usually not serious beyond about 150 m (500 ft) from heavy freeways or 30-60 m (100-200 ft) from lightly traveled roads.⁹

Weather bends sound too, an effect the FHWA calls atmospheric refraction. Downwind, sound is bent toward the ground and levels rise; upwind, it is bent away and levels fall, and studies cited by the FHWA measured wind effects of up to 7 dB(A) within 100 m of a road.⁵ On a sunny day, warm air near the ground bends sound upward; at night, a temperature inversion - cool air under warmer air - bends it back down and can raise levels at a listener, though the FHWA says temperature effects are not substantial within about 61 m (200 ft) of a road.⁵

Do noise barriers work?

What you hear: the tall concrete walls along a highway, and the quieter yards behind them.

Yes, within limits. The FHWA's handbook says a barrier that barely breaks the line of sight between road and listener gives about 5 dB(A) of reduction, a good barrier approaches 10 dB(A), and the practical maximum is about 20 dB(A) for walls and 23 dB(A) for earth berms.⁵ A row of buildings gives about 3 dB(A), plus about 1.5 dB(A) for each extra row, and a dense belt of vegetation 5 m tall and 30 m wide can give up to 5 dB(A).⁵ A barrier material of 20 kg/m2 or more provides at least 20 dB(A) of transmission loss, so the wall itself is rarely the weak point - sound bending over the top is.⁵

Why can I hear bass through my wall but not voices?

What you hear: the neighbor's subwoofer thumps clearly; the words of the song are gone.

Walls stop sound mainly by mass, and the mass law says transmission loss rises about 6 dB for each doubling of frequency and about 6 dB for each doubling of the wall's surface mass.⁸ Run that backward and the same wall blocks about 6 dB less every time the pitch halves. An acoustics firm's example: a single layer of 5/8-inch drywall that blocks 40 dB at 1 kHz would block about 34 dB at 500 Hz, 28 dB at 250 Hz and 22 dB at 100 Hz.⁸ Voices and treble get knocked down hard; bass does not.

There is a second problem. Typical two-layer drywall walls have a mass-air-mass resonance, a frequency where the wall flexes like a drum, usually around 50-100 Hz.⁸ The common US wall rating, STC (Sound Transmission Class), is averaged over 125-4,000 Hz, so that weak spot can sit below the range the rating checks.⁸ A wall with a respectable STC can still pass a kick drum, which is why bass is the usual complaint between neighbors and venues (see nightlife).

Finally, long bass waves travel through structure. They couple into floor slabs and stud cavities and go around the wall, a path called flanking, and door seals that help with speech do little for bass.⁸ These figures come from an acoustics vendor, not a standards body.

What do hard walls and tall buildings do?

What you hear: a siren that seems to come from everywhere at once on a narrow downtown street.

Hard, flat surfaces reflect sound rather than absorbing it. Tall facades keep throwing sound back into the street instead of letting it spread. The verified evidence is indirect: the FHWA reports that two parallel reflective highway barriers can degrade each other's performance by 2-6 dB(A), that reflections from an opposing barrier typically add 1-2 dB(A), and it recommends a width-to-height ratio of 10:1 or more to keep the effect small.⁵ A narrow street between tall buildings is a much tighter ratio than that.

One peer-reviewed estimate: a 2010 paper by Okada, Yoshihisa and Kuno in Acoustical Science and Technology modeled street canyons with an elevated road, checked against a 1:40 scale model, and put the mean increase from multiple reflections between buildings at "up to about 8 dB" in built-up urban areas.¹³ That figure is for one street layout and a modeled average, not a rule for every downtown block.

What is a sound level meter, and what is Class 1?

What you hear: nothing - but this is the instrument a city inspector or acoustic consultant brings.

Professional meters are graded under the international standard IEC 61672-1 as Class 1 (precision) or Class 2 (general purpose). The older US terms under ANSI S1.4 are Type 1 and Type 2, and both are still in use.¹⁴ At 1 kHz the tolerance is +/-1.1 dB for Class 1 and +/-1.4 dB for Class 2; at 20 Hz it is +/-2.5 dB versus +/-3.5 dB, and the gap widens at high frequencies.¹⁵ OSHA treats a Type 2 meter as accurate to +/-2 dBA.¹⁴

Which class is required depends on the job. In the UK, the Control of Noise at Work Regulations 2005 require at least Class 2, while ISO 20906 for unattended aircraft noise monitoring requires Class 1.¹⁵ The tolerance figures above come from a meter manufacturer rather than the standard itself, which is behind a paywall.

Is a phone decibel app accurate?

What you hear: your own phone telling you the bar is at 94 dB.

Some are good; many are not. In 2014, NIOSH researchers examined 130 iOS apps and tested 10, and examined 62 Android apps, of which only 4 "partially met" their criteria.¹⁶ Three iOS apps came within +/-2 dBA of a reference meter.¹⁶ The best, SoundMeter, averaged -0.51 dBA off. A single Android app showed "wide variance" from phone to phone, and the authors concluded that Android and Windows apps did not meet occupational needs.¹⁴ A 2015 follow-up found that with a calibrated external microphone, apps agreed within +/-1 dB of professional instruments, and NIOSH announced plans for its own free app.¹⁷

That app, the NIOSH Sound Level Meter, was announced in a NIOSH blog post dated January 2017. It reports LAeq, Lmax, Lpeak, time-weighted average and noise dose.¹⁰ In a 2019 evaluation, it read about 2 dBA off with an iPhone's built-in microphone in lab pink-noise tests and within 1 dBA with a calibrated external microphone; in an underground mine it was within about 2 dBA.¹⁰

As of its last review (February 16, 2024), NIOSH's app page says the app "is only available on iOS devices," and that "verifying the accuracy of an Android-based app is not currently possible" in its lab.¹⁸

A good iPhone app is fine for awareness - knowing whether a room is in the 70s or the 90s. For anything formal, a calibrated Class 1 or Class 2 meter is what counts.

How loud is loud? A rough decibel ruler

What you hear: everything on one scale.

The American Academy of Audiology's 2023 poster lists rustling leaves at 20 dB, a whisper at 30, a quiet library at 40, moderate rainfall at 50, normal conversation at 60, traffic at 70, an alarm clock at 80, a lawnmower at 90, earbuds at full volume at 100, concerts and car horns at 110, a jet at takeoff at 120, a jackhammer at 130 and fireworks at 140 dB.¹⁹ The poster gives no weighting and no distance, so treat it as a sense of scale, not as measurements to compare with a meter reading.

NIOSH offers a more practical yardstick: if you have to raise your voice to be heard by someone about 3 ft (1 m) away, the level is likely 85 dBA or more; if you have to shout, it is likely 95 dBA or more.²⁰ NIOSH's recommended workplace limit is 85 dBA averaged over 8 hours,²⁰ with allowed time halving for every 3 dB above that.²¹ At the other end, the NIDCD says sounds at or below 70 dBA are unlikely to cause hearing loss even after long exposure.²² The health section covers what those limits mean.

What is a noise map?

What you hear: nothing - a noise map is a model, not a recording.

Noise maps are computer models of long-term average levels from roads, rail and aircraft. In the US, the Bureau of Transportation Statistics released its first National Transportation Noise Map on March 21, 2017, modeling aviation and Interstate highway noise as a 24-hour LAeq from 2014 data.²³ It found more than 97% of the US population potentially exposed to transportation noise below 50 dBA.²³ BTS describes the modeling as worst case, with no shielding from buildings or terrain, and meant for tracking trends rather than assessing impact at any one home.²³

In Boston

The national BTS map models aviation and Interstate noise across the whole country,²³ so Boston's Interstates and Logan Airport fall inside it. Because DNL is the standard metric for all FAA aviation noise studies,⁴ any FAA noise study around Logan reports in DNL, not in the Lden figures used in European cities. The physics in this section is the same on a Boston side street as anywhere else: a single horn fades about 6 dB(A) per doubling of distance, a highway only about 3 dB(A).

What Boston does have is modeled Logan contours. According to the Massachusetts Department of Public Health's Logan Airport Health Study (May 2014), Massport produces annual DNL contours around Logan ranging from 60 to 75 dBA in 5 dB steps, using the FAA's Integrated Noise Model.²⁴

Elsewhere in the world

The physics is universal; the paperwork is not. The US uses DNL for aviation and Leq(h) or L10 on highways,⁹ while the EU uses Lden and Lnight.¹² EU law requires strategic noise maps every five years for large cities and major roads, railways and airports, where the US federal map is voluntary.¹² EU maps estimate how many people are annoyed (from Lden) and sleep-disturbed (from Lnight), and the Directive itself "does not set any limit value."²⁵ Meter standards split along the same line: US practice often cites ANSI Type 1 and Type 2, and the UK and Europe cite IEC 61672 Class 1 and Class 2.¹⁵

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03What noise does to your ears, sleep and heart

The short version: Loud sound damages hearing through a mix of level and time: in the US, the federal research agency NIOSH recommends no more than 85 dBA averaged over 8 hours, and every 3 dB louder halves that time, so 100 dBA is a 15-minute dose. Quieter, long-term noise from traffic and aircraft is linked by WHO and the European Environment Agency to annoyance, broken sleep, heart disease and slower reading in children, mostly as population-wide statistics rather than individual verdicts. WHO's 2018 guidelines set outdoor targets by source, with the strictest night value for aircraft.

This section reports what NIOSH, OSHA, NIDCD, CDC, WHO and the EEA say. It is not medical advice. For your own hearing, sleep or heart, ask a doctor or audiologist and read the agency pages in the footnotes.

How loud is too loud for your ears?

What you hear: a lawn mower, a hand dryer, a club, a siren going past.

Hearing damage depends on how loud a sound is and how long you are in it. Workplace rules express this as a time-weighted average (TWA) - your exposure averaged over a shift, usually 8 hours - plus an exchange rate, the number of decibels that halves the allowed time.

The US has two numbers, and they disagree:

• NIOSH, the federal research agency, sets a Recommended Exposure Limit (REL) of 85 dBA as an 8-hour TWA with a 3 dB exchange rate: each 3 dBA increase halves the allowable time.²¹ This is advice, not law. NIOSH recommends hearing protection whenever noise is above 85 dBA regardless of how long, and notes that about 8% of workers could still develop hearing loss at 85 dBA.³ ACGIH uses the same 85 dBA and 3 dB.²⁶
• OSHA, the enforcement agency, sets a Permissible Exposure Limit (PEL) of 90 dBA as an 8-hour TWA with a 5 dB exchange rate. At 85 dBA TWA - its action level - general industry, maritime and longshoring employers must run a hearing conservation program; construction uses 90 dBA.²⁷ OSHA's impulsive or impact noise ceiling is 140 dB peak sound pressure level.²⁸

CDC estimates about 22 million US workers are exposed to potentially damaging noise each year.²⁷

A field test you can do without a meter: if you have to raise your voice to be heard by someone about 3 ft (1 m) away, the level is likely 85 dBA or more; if you have to shout, it is likely 95 dBA or more.²⁰

For everyday, non-work life, NIDCD says sounds at or below 70 dBA are unlikely to cause hearing loss even after long exposure.²² In 1974 the US EPA identified 70 dBA averaged over 24 hours (about 75 dBA over 8 hours) as protective of hearing, and 55 dBA outdoors and 45 dBA indoors to avoid speech interference and annoyance - and said these were not regulations.²⁹

How long can I listen at 100 decibels?

What you hear: a loud concert, headphones turned all the way up, a crowd at a big game.

At 100 dBA, NIOSH's recommended daily limit is 15 minutes; OSHA's legal limit is 2 hours.²⁹²⁸ NIDCD says damage is more likely after at least 14 minutes at 100 dBA and 2 minutes at 110 dBA.³⁰

Daily unprotected exposure, by agency. Values without "calc." are printed by the agency; "calc." values are our arithmetic using each agency's stated exchange rate (NIOSH 3 dB, OSHA 5 dB) and are not printed in the source tables.²⁹²⁸

Doses add up across the day: half an hour at 97 dBA uses a full NIOSH daily allowance. For sound systems and concert levels from the engineer's side, see The Show File.

How many people already have noise damage?

What you hear: nothing unusual - which is the point.

CDC's 2017 Vital Signs report, using 2011-2012 national hearing tests, found an audiometric notch - a dip in the hearing test typical of noise damage - in 24.4% of US adults aged 20 to 69, about 39.4 million people. Among adults with no loud work exposure, 19.9% had one, and so did 23.5% of people who rated their own hearing excellent or good.³ CDC's summary adds that about 53% of people with noise damage report no on-the-job exposure, and that hearing loss is the third most common chronic condition in the US.³¹

NIDCD frames the range more cautiously: at least 10 million (6%) and up to 40 million (24%) US adults under 70 (2011-2012 data), plus up to 17% of teens aged 12 to 19 (2005-2006 data), showing signs suggestive of noise-induced hearing loss (NIHL).²² NIDCD calls NIHL "the only type of hearing loss that is completely preventable."²²

WHO estimates 1.1 billion young people are at risk of hearing loss from unsafe listening, and that 40% of 12- to 35-year-olds in middle- and high-income countries are exposed to damaging levels at entertainment venues.³²

WHO's deafness and hearing loss fact sheet (updated 3 March 2026) puts the number of people worldwide who need rehabilitation for disabling hearing loss at 430 million, including 34 million children, and projects that nearly 2.5 billion people will have some degree of hearing loss by 2050, with more than 700 million needing rehabilitation.³³

Does tinnitus from a concert go away?

What you hear: ringing, buzzing or roaring that nobody else can hear.

Tinnitus is hearing sound with no outside source. NIDCD says loud noise can cause tinnitus that may fade, or in some cases last for life.²² Noise is one known cause, not the only one.

A 2022 global meta-analysis by Jarach and colleagues in JAMA Neurology pooled studies to estimate that 14.4% of adults have tinnitus (95% confidence interval 12.6-16.5%), and 2.3% have it severely - more than 740 million adults worldwide, with more than 120 million perceiving it as a major problem.³⁴ Prevalence rose from almost 10% at ages 18 to 44 to almost 24% at 65 and older.³⁵

For the US, NIDCD's quick statistics page, citing a 2016 study by Bhatt and colleagues in JAMA Otolaryngology-Head & Neck Surgery, says roughly 10% of US adults, or about 25 million people, have had tinnitus lasting at least 5 minutes in the past year.³⁶

What are the WHO noise guidelines?

What you hear: the steady wash of a highway, trains, planes on approach.

In 2018 WHO Europe published recommended levels, by source, for long-term outdoor noise at the home. They use Lden, a 24-hour average with 5 dB added to evening and 10 dB to night sounds, and Lnight, the average over the night period. Both are annual averages measured outside, so they cannot be compared directly with a dBA reading from a phone app.

Values and strength labels are from the executive summary of the guidelines document itself, WHO Regional Office for Europe, "Environmental noise guidelines for the European Region" (ISBN 978 92 890 5356 3), where "strong" and "conditional" are the guideline group's own grades.³⁷ WHO gave no night value for wind turbines because "the quality of evidence of night-time exposure to wind turbine noise is too low to allow a recommendation."³⁷

A 2022 WHO compendium repeats the night values and links excessive noise to heart disease, hypertension, sleep disturbance, hearing impairment, tinnitus and cognitive impairment.³⁸

These are guidelines, not law. The EU's own reporting thresholds (55 dB Lden, 50 dB Lnight) sit above them, which is why the EEA reports exposure against both.²

What decibel level is safe for sleeping?

What you hear: a truck downshifting at 3am, a late flight, a neighbor's bass.

WHO's 2009 Night Noise Guidelines for Europe set 40 dB Lnight,outside - an annual average at the facade - as the target to protect the public, including children, the chronically ill and the elderly. Countries that could not reach 40 dB in the short term were given an interim target of 55 dB.³⁹ It was WHO's main night value until the 2018 source-specific numbers.

As reported by IEMA, the 2009 guidance laid out effect thresholds: below 40 dB, not enough evidence of harm; 42 dB, a threshold for waking at night or too early; 50 dB, a threshold reported for heart attacks; above 55 dB, cardiovascular effects become "a major health concern." Evidence was rated strong for arousal, sleep-stage changes and awakening, and limited for hypertension, heart attacks and depression.⁴⁰ Noise can change sleep stages without fully waking someone.

The EEA's 2025 report estimates that each year transport noise leaves about 4.6 million Europeans severely sleep disturbed and almost 16.9 million long-term annoyed - annoyance being a health outcome measured with standardized surveys.² An earlier EEA estimate on a different scope gave 5.5 million highly sleep disturbed and 18.4 million highly annoyed.⁴¹

Why do restaurants get so loud?

What you hear: a room that gets louder every half hour until you are shouting across the table.

People automatically raise their voices in noise - and change pitch and pace - which is called the Lombard effect. A 2011 review by Brumm and Zollinger in Behaviour, marking 100 years since the effect was described, traced it across humans and animals and suggested it may date back more than 300 million years.⁴² In a crowded room, each table talks over the others, which raises the level for everyone.

Can traffic noise cause heart disease?

What you hear: nothing you would connect to your heart - years of a busy road outside.

The evidence comes from observational population studies, which show associations, not proof of cause in any one person.

• A WHO-commissioned systematic review (van Kempen and colleagues, 2018) found high-quality evidence that road traffic noise is associated with ischaemic heart disease, with a relative risk of 1.08 (95% CI 1.01-1.15) per 10 dB Lden across seven longitudinal studies - about an 8% higher risk. The same review rated hypertension studies as mainly cross-sectional with high risk of bias, and the evidence on stroke, diabetes and obesity as moderate to very low depending on the noise source.⁴³
• The EEA, in March 2025, described newer studies as "consolidating" links between transport noise (especially road) and ischaemic heart disease, stroke and heart failure, and type 2 diabetes. It called evidence for depression, dementia and cancer limited or emerging, and said some effects are seen from 45 dB Lden.⁴¹

Most cohort studies are European. For the road side of this, see traffic noise. A relative risk of 1.08 is small for an individual and adds up mainly across very large populations.

The WHO review's own authors flagged the limits: beyond the ischaemic heart disease finding, they described the available studies as mostly cross-sectional and "suffering from a high risk of bias," and they concluded that "we need more and better quality evidence, primarily based on longitudinal studies."⁴⁴

How many people are affected in Europe?

What you hear: the background of most cities.

The European Environment Agency's report Environmental noise in Europe 2025 (published 24 June 2025, data year 2022, with a corrigendum to the health figures added 27 March 2026) estimates:²

• More than 20% of Europeans live with transport noise at or above 55 dB Lden, and more than 30% when measured against WHO's levels.
• Road noise affects about 92 million people at that level, rail about 18 million and aircraft about 2.6 million.
• Each year: 73,000 premature deaths, about 49,000 new cardiovascular disease cases, 23,000 new type 2 diabetes cases, and 1.5 million healthy life years lost (years of healthy life lost to illness, disability or early death).
• An economic cost of at least EUR 100 billion a year, about 0.6% of GDP.

The EEA's separate indicator (3 October 2025, same data year) gives about 89 million for road at 55 dB Lden or above and 57 million at 50 dB Lnight or above.⁴⁵ The EEA judges the EU's goal of cutting chronically disturbed people by 30% by 2030 unlikely to be met.²

Do airplanes affect children's learning?

What you hear: a classroom that pauses every few minutes for a jet.

The RANCH study, published in The Lancet in 2005 by Stansfeld and colleagues, compared children near airports in three countries.⁴⁶ It covered more than 2,800 children aged 9 to 10 at 89 primary schools near Schiphol, Barajas and Heathrow. Higher aircraft noise was linked to reading-age delays of up to two months in the UK and one month in the Netherlands; road traffic noise did not affect reading and was linked to better recall memory.⁴⁷

A 2017 National Academies (ACRP) review counted more than 20 studies finding aircraft noise harms children, most strongly for reading. It cites a US pilot study by FICAN (2004, 35 schools near three airports) linking noise reduction to fewer failing high-school students, and an ACRP study (2014) finding a significant relationship between aircraft noise and test scores.⁴⁸ The EEA attributes reading difficulties in over 500,000 European children, and behavioral issues in about 115,000, to transport noise.² Flight paths and airport noise rules are in the aircraft section.

What is misophonia vs hyperacusis?

What you hear: ordinary sounds that feel painfully loud, or one particular sound - chewing, breathing - that is hard to bear.

Both describe reduced tolerance to sound; definitions and treatment are still debated.

• Hyperacusis: the ICD-10 code H93.23 describes it as "an abnormally disproportionate increase in the sensation of loudness in response to auditory stimuli of normal volume." Clinicians Jastreboff and Jastreboff (2023) describe it as a reaction that depends only on a sound's physical characteristics.⁴⁹
• Misophonia: a 2022 expert panel (Swedo and colleagues, using a modified Delphi process with an 80% agreement rule) produced the first consensus definition: "a disorder of decreased tolerance to specific sounds or their associated stimuli."⁵⁰ Jastreboff and Jastreboff describe it as depending on a sound's meaning and context rather than its loudness.⁴⁹

Population figures are scarce. For misophonia in the US, a 2025 presentation by Dixon, posted by Duke University's psychiatry department, reports that 4.6% of a random household sample of 4,005 US adults, described as representative of the adult population by Census measures, met criteria for misophonia.⁵¹

Are there safe listening standards for headphones and venues?

What you hear: a phone warning that you have hit your weekly listening limit; a festival with a quiet tent.

WHO and the International Telecommunication Union published a voluntary standard for personal audio, ITU-T H.870 (2019). Devices track a weekly "sound allowance" against a reference exposure: 80 dB for 40 hours a week for adults (Mode 1) and 75 dB for 40 hours a week for children (Mode 2). Its features include dosimetry, a personal listening profile, automatic volume limiting and parental volume control.⁵²

In 2022 WHO added a Global standard for safe listening venues and events, with six features: cap average levels at 100 dB LAeq over any 15 minutes; monitor continuously with designated staff and calibrated equipment; optimize acoustics and sound systems; provide hearing protection; offer quiet zones; and provide training and information.³² Both standards are voluntary unless a government writes them into law. How venues and neighbors negotiate sound is covered in nightlife.

In a September 2022 CDC survey of 4,514 US adults, 54.1% agreed venue sound levels should be limited, 75.4% wanted warning signs, and 61.2% said they would wear hearing protection if provided.⁵³

What NRR earplugs do I need for a concert?

What you hear: the show, a bit duller - or no change at all if the plugs are not in properly.

US hearing protectors carry a Noise Reduction Rating (NRR), required by the EPA on labels since 1979. It comes from lab tests on 10 subjects and was meant to predict the minimum protection for 98% of users.⁵⁴ Real-world protection is usually lower: OSHA's technical manual says labeled NRRs often overstate actual protection because most workers are not fit-tested,⁵⁵ and a 1996 review of 22 field studies found labels overestimated real protection by 5% to 2000%.⁵⁴

So agencies "derate" the label:

• OSHA Appendix B: with dBA measurements, subtract 7 from the NRR, then subtract the result from the A-weighted TWA.²⁸ OSHA guidance also applies a further 50% safety factor.⁵⁴
• NIOSH counts earmuffs at 75% of the NRR, formable foam plugs at 50% and other plugs at 30%.⁵⁴

A worked example (our arithmetic): foam plugs labeled NRR 33 at a 100 dBA show. OSHA's method gives 100 - (33 - 7) = 74 dBA as a lab-style estimate; with the 50% safety factor, (33 - 7) / 2 = 13, so about 87 dBA at the ear - still above the 85 dBA level at which NIOSH recommends hearing protection.

NIDCD stresses that fit matters: plugs must be inserted properly, cutting foam plugs reduces protection, and custom musician's earplugs let in more natural sound.⁵⁶

In Boston

The rules in this section are national: in Boston, as across the US, OSHA's 90 dBA PEL and 85 dBA action level are the federal workplace rule, and NIOSH's 85 dBA REL is the federal health recommendation.²⁷²¹ The WHO and EEA figures are European and are not limits in Massachusetts.

The Massachusetts study closest to these questions is the Department of Public Health's Logan Airport Health Study (May 2014), which covered 17 communities fully or partly within five miles of the airport, including Boston. It grouped residents by Massport's modeled aircraft noise contours - 65 dBA DNL and above as high exposure, 60-64 dBA as medium, below 60 dBA as low - and found "no statistically significant differences with respect to hearing loss" between the high and lowest exposure areas, for adults or children.²⁴ Its elevated respiratory findings were tied to modeled air pollution, not noise, and it found no statistically significant differences in cardiovascular outcomes.²⁴

Elsewhere in the world

• Europe: the EEA reports exposure against both the EU's 55 dB Lden threshold and WHO's stricter values.²
• Global: the WHO-ITU device standard (2019) and WHO venue standard (2022) are written for any country to adopt.⁵²³²

Where to go for help

Start with a doctor or audiologist. For public references: NIDCD on hearing loss and protectors,²²⁵⁶ NIOSH and OSHA on workplace exposure,²¹²⁷ and the EEA on Europe's figures.²

Report an error in this section

04Who makes the noise rules

The short version: In the United States, nearly every noise rule a resident runs into - quiet hours, bar music, construction start times, leaf blowers - is written by a city or town, largely because Congress stopped funding the federal noise office in 1981. Local codes mix quiet hours, "plainly audible" tests that need no meter, and decibel limits measured at a property line or inside a home, usually stricter at night. Other countries split the job differently: England and Wales put a legal duty on councils to investigate "statutory nuisance," the EU requires noise maps but sets no limits, and Japan sets national target levels by type of area.

Why is there no national noise law in the US?

There is one on paper. The Noise Control Act of 1972 and the Quiet Communities Act of 1978 told the Environmental Protection Agency to study and regulate noise, and EPA set up the Office of Noise Abatement and Control (ONAC) to do it.⁵⁷ The 1978 law added grants for state and local noise programs.⁵⁸ In 1981 Congress agreed to "cease funding for the Office of Noise Abatement and Control," and EPA stopped nearly all noise work.⁵⁸ Sources differ slightly on the end date: an ACUS consultant's report quotes one official's account that EPA's noise staff fell from 175 to zero, and notes that one federal panel dated the office's elimination to 1982.⁵⁹

The law was never repealed. The federal product noise standards EPA had already issued stayed in force and still preempt (block) different state and local standards for those products, but nobody was left to update them, so they froze in place.⁵⁸ The Act preempts state and local emission standards for EPA-regulated products, not local rules on how and when things are used or operated⁵⁹ - which is why your city can set hours for construction or lawn equipment. In 1992 the Administrative Conference of the United States told Congress to either repeal the Act or fund it.⁵⁸

A 2023 lawsuit, Quiet Communities, Inc. v. EPA, brought with the involvement of law professors Sanne Knudsen and Jeff Feldman, challenged EPA's more than 40 years of failing to carry out the statutes, and Judge Jia M. Cobb ruled for the plaintiffs.⁵⁷ The July 2026 ruling found EPA "has unlawfully neglected its legal obligation" under the 1972 Act, sided with the plaintiffs on four of nine claims, and left remedies to separate proceedings.⁶⁰

As of a post-ruling summary dated August 20, 2026 by the consulting firm Trinity Consultants, the remedy had not been determined: the court will next decide what steps EPA must take and on what timeline, and the ruling itself sets no new noise limits or compliance requirements.⁶¹

Aircraft and workplace noise have their own federal rules: see the aircraft section for flight paths and airport noise, and the health section for OSHA and NIOSH workplace limits. How cities got here is told in the history section.

How does a typical city noise ordinance work?

Most US and Canadian codes combine four tools, often in the same chapter.

Many places also vary limits by type of area, as Japan does,⁶⁶ and most carry separate rules for construction, power equipment, vehicles, air conditioners, animals and amplified music.

What does "plainly audible" mean?

A plainly audible (or "clearly audible") standard is broken if a person can clearly hear the sound from a defined spot. New York City says heavier vehicles and motorcycles "should not be audible 200 feet away."⁶³ Toronto bans "clearly audible" construction noise from 7 p.m. to 7 a.m. (to 9 a.m. on Saturdays) and all day on Sundays and statutory holidays.⁶⁷ New South Wales, Australia, puts the test indoors: listed equipment "should not be heard inside a habitable room of a neighbour's residence" during restricted times.⁶⁸

Where is the noise measured?

The same sound can pass or fail depending on where the reading is taken - the point of reception.

• At the property line. Boston measures at the residential lot line or the nearest affected dwelling.⁶² Since February 2024, Toronto can also measure from the property line.⁶⁹
• Inside the complainant's home. New York City's 42 dB(A) music limit applies in the receiving dwelling,⁶⁴ and England's night-noise test is measured inside the complainant's home.⁷⁰
• Against the background. The ambient level is the sound present without the noise being complained about. San Francisco's night construction rule and New York City's night rule both measure a source's excess over ambient.^{65 64}

Most limits use dBA, which filters sound roughly the way human hearing does. Because A-weighting turns down bass, New York City and Toronto add dBC limits, which keep the low end, to catch thumping music.^{64 67}

What are New York City's noise rules?

New York City rewrote its 1972 noise code through Local Law 113 of 2005, passed by the City Council on December 21, 2005, signed on December 29, and in effect from July 1, 2007.⁶⁴ The city's Department of Environmental Protection notes that the revised code took effect 30 years after the original was introduced.⁶³

The noise mitigation plan is the city's tool for working construction sites: a written plan for how the site will reduce noise. If after-hours site noise exceeds 8 dB(A) above ambient inside a home with the windows closed, the commissioner can demand changes.⁶⁴

Noise is the city's top 311 issue. 311 took more than 738,000 noise complaints in 2024 - over 2,000 a day - led by residential noise at more than 356,000.¹

Fines are set in DEP's Noise Penalty Schedule. A first violation of the general unreasonable-noise rule (24-218) carries a standard penalty of $350 from 7 a.m. to 10 p.m. and $450 from 10 p.m. to 7 a.m.; bar or club music above the limits (24-231) is $3,200; construction at impermissible times (24-222) is $1,400; and an animal making unreasonable noise (24-235) is $70.⁷¹ Penalties rise with each repeat - a third commercial music violation is $9,600 - and the schedule lists higher default amounts, up to $24,000 for that offense.⁷¹

What about San Francisco?

What you hear: a concrete pour or saw cutting after dark.

San Francisco's rules sit in Police Code Article 29. Powered construction equipment may not exceed 80 dBA at 100 feet (Section 2907).⁶⁵ From 8 p.m. to 7 a.m., construction may not exceed the ambient level by more than 5 dBA at the nearest property line unless the Director of Public Works issues a special permit with conditions (Section 2908).⁶⁵ That makes the ordinary construction day effectively 7 a.m. to 8 p.m., two hours longer than New York City's weekday window.⁶⁴

Who bans leaf blowers, and why is it contested?

What you hear: a two-stroke whine that rises and falls as the operator sweeps.

Leaf blower rules began as noise ordinances in California towns: Carmel-by-the-Sea in 1975 and Beverly Hills in 1978.⁷² Newer rules target gas engines for both noise and air pollution. Washington, DC's gas-blower ban, passed in 2018, took effect January 1, 2022; Cambridge, Massachusetts, banned gas blowers in 2025; and Portland, Oregon, is phasing them out from 2026, with a ban in 2028.⁷²

California went after sales instead of use: AB 1346, by Assemblymember Marc Berman, passed in October 2021 and halts sales of most new gas leaf blowers, mowers and other small off-road engines from 2024 (generators from 2028). Existing equipment can be used indefinitely, and the bill "barely passed."⁷³ Other places only set hours, such as New South Wales (8 p.m. to 7 a.m. on weekdays under its 2017 rules)⁶⁸ and Toronto (power devices barred 7 p.m. to 8 a.m.).⁶⁷

A 2016 study of North Carolina university groundskeepers found leaf blower noise averaged 89 dB(A) and peaked at 106 dB(A); the distance was not given.⁷²

Supporters cite noise and emissions. Doug O'Malley of Environment New Jersey said one hour of use pollutes as much as driving a car 1,100 miles, and a Montclair, New Jersey, ban advocate said the town became "healthier, cleaner, quieter."⁷⁴ Landscapers cite cost and performance. Rich Goldstein, president of a New Jersey landscaping trade association, said his firm owns $150,000 to $200,000 in gas blowers ("What am I supposed to do, throw them in the garbage?"), that battery models are less capable, and that charging means retrofitting trucks; landscapers challenged Montclair's ban in court.⁷⁴ The machines themselves, and how loud they are, are covered in construction, backup beepers and leaf blowers.

In Boston

Boston's ordinance treats noise above 50 dBA from 11 p.m. to 7 a.m., or above 70 dBA at other hours, as unreasonable at a residential lot line.⁶² Who enforces what, construction hours and after-hours permits are covered in the Boston section.

Elsewhere in the world: how the rules compare

These numbers use different metrics, measurement points and averaging times, so they are not directly comparable: 42 dBA inside a home and 50 dBA at a lot line describe different situations.

How does the UK deal with noisy neighbors?

In England and Wales, noise is a statutory nuisance if it "unreasonably and substantially" interferes with the use or enjoyment of a home or other premises, or injures health. If a council finds one, it must serve an abatement notice, which can be delayed up to 7 days.⁷⁰ Section 79 of the Environmental Protection Act 1990 puts a duty on councils to reasonably investigate complaints, and ignoring an abatement notice is an offence.⁷⁷

The Noise Act 1996 adds a measured night test from 11 p.m. to 7 a.m.: inside the complainant's home, the permitted level is 34 dBA where underlying noise is 24 dBA or less, or 10 dBA above the underlying level where it is higher. Fixed penalties run up to £110 for homes and £500 for licensed premises; on conviction, up to £1,000 for homes and unlimited for licensed premises, and councils can seize equipment.⁷⁰ Councils choose their own service level, including whether officers are on call at night.⁷⁰

Specific offences cover street loudspeakers, fireworks between 11 p.m. and 7 a.m. (with festival extensions), and ice cream van chimes outside noon to 7 p.m., with a code of practice on how chimes should be used.⁷⁷

What time can builders start in the UK?

Construction falls under the Control of Pollution Act 1974. After a substantiated complaint, a council can serve a section 60 notice setting hours and conditions. A builder can instead apply, at least 28 days ahead, for section 61 prior consent, agreeing methods in advance under "Best Practicable Means." Breaching consent conditions is an offence, and appeals go to a Magistrates' Court within 21 days.⁷⁵ Hours are set council by council; Monday to Friday 8 a.m. to 6 p.m. and Saturday 8 a.m. to 1 p.m. is a common pattern, not national law.⁷⁵

Does the EU set noise limits?

No. The Environmental Noise Directive (2002/49/EC), adopted June 25, 2002, sets reporting thresholds, not limit values.⁷⁶ Member states must produce strategic noise maps every five years for major roads (over 3 million vehicle passages a year), railways (over 30,000 train passages a year), airports (over 50,000 movements a year) and cities over 100,000 people, count how many people live above Lden 55 dB and Lnight 50 dB in 5 dB bands, adopt action plans, and preserve quiet areas.⁷⁶ Limits are set by each country or city; what Lden and Lnight mean is explained in sound and decibels.

What are Toronto's noise limits?

Toronto's Chapter 591 was adopted June 19, 2019 and took effect October 1, 2019.⁶⁷ Amplified sound is measured as an Leq over 10 minutes at the point of reception: outdoors, 55 dB(A) or 70 dB(C) from 7 a.m. to 11 p.m. and 50 dB(A) or 65 dB(C) overnight; indoors, 50 dB(A) / 65 dB(C) by day and 42 dB(A) / 57 dB(C) at night.⁶⁷ Stationary sources, including home air conditioners, are limited to 50 dB(A) by day and 45 dB(A) at night outdoors, over one hour. Vehicle exhaust is capped at 92 dB(A) at idle and 96 dB(A) above idle, measured 50 cm from the outlet.⁶⁷

On February 7, 2024, Council cut the indoor night limits from 45 to 42 dB(A) and 60 to 57 dB(C), allowed measurement from the property line, added limits for unamplified instruments such as drums, and added sound-induced vibration and tonal qualities like hiss, hum and buzz.⁶⁹

What time can you mow the lawn in New South Wales?

Under the Protection of the Environment Operations (Noise Control) Regulation 2017, which replaced a 2008 version and was in force until August 28, 2026 (see below for its replacement),⁷⁸ common household sources were not to be heard inside a neighbor's habitable room at these times:⁶⁸

Under the same 2017 rules, intruder alarms should stop after 5 minutes if installed on or after December 1, 1997, or 10 minutes if older.⁶⁸

Those times come from the 2017 Regulation, which was replaced by the Protection of the Environment Operations (Noise Control) Regulation 2026 on August 28, 2026, with higher penalties for noise from vehicles, vessels and common neighborhood sources.⁷⁹ The new rules extend the permitted hours for residential air conditioners and pumps, exempt air conditioners from the restricted hours during severe or extreme heatwaves, and raise most noise penalties by a third.⁸⁰ The draft proposed moving the night-time limit for pool and spa pumps from 8 p.m. to 9 p.m.;⁸¹ check the final times with your council before relying on the pump and air-conditioner rows above.

What are Japan's noise standards?

Japan's Environmental Quality Standards for Noise were issued under the Basic Environment Law on September 30, 1998 and enforced from April 1, 1999. They are targets, graded by area type, with day running 6 a.m. to 10 p.m. and night 10 p.m. to 6 a.m. Levels are equivalent continuous A-weighted (LAeq).⁶⁶

The standards exclude aircraft, railway and construction noise, which are covered separately.⁶⁶

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05A short history of city noise

The short version: People have complained about city noise for as long as there have been cities: a Roman poet blamed night-time wagons for sleepless nights around 100 CE. Modern noise control grew out of campaigns by individuals - Charles Babbage against London's organ grinders in the 1860s, Julia Barnett Rice against New York's tugboat whistles in 1906 - and New York's 1929-1930 Noise Abatement Commission was among the first to measure street noise in decibels. The US passed a federal Noise Control Act in 1972, then stopped funding the office that ran it in the early 1980s, leaving noise largely to states and cities, while the EU went the other way with a 2002 directive requiring noise maps. Alongside the rules, a Canadian composer's idea of the "soundscape" changed the question from how to remove noise to which sounds are worth keeping.

Did ancient Rome have noise laws?

What you hear: wagon wheels on stone, all night.

Not exactly - but Rome had a traffic law that shaped its night sound. A text known as the Law of Caesar on Municipalities, dated 44 BCE, says that "no one shall drive a wagon along the streets of Rome" after sunrise or before the tenth hour of the day.⁸² It made exceptions for wagons hauling materials to build temples and public works, for carting away rubbish from publicly contracted demolitions, and for sacred processions, triumphs and public games; wagons that had come in at night could leave empty or carry out dung.⁸² The point was congestion in daytime streets, not quiet. Its side effect was to push delivery traffic into the night.

The poet Juvenal, writing around 100 CE, described the result. In his third Satire he asks, "Show me the apartment that lets you sleep!", describes wagons thundering through narrow streets after dark, and says that "insomnia causes most deaths here."⁸³ Sleep in the city, he says, takes great wealth.⁸⁴ Juvenal was a satirist, so the death toll is a joke, but the complaint - that the city's delivery schedule decided when its residents slept - would be familiar to anyone near a loading dock today.

Babbage against the organ grinders (London, 1860s)

What you hear: a barrel organ starting up under your window, again.

The mathematician Charles Babbage spent years at war with London's street musicians. In his 1864 Chapter on Street Nuisances he recorded 165 interruptions to his work over 80 days and estimated that street noise cost him a quarter of his working power.⁸⁵ The campaign made him a target: neighbors hired musicians to play outside his house.⁸⁵

He was not alone. Charles Dickens backed the cause, and Babbage's pamphlet appeared alongside a campaign in Parliament by MP Michael Bass. The law known as Bass's Act passed later in 1864.⁸⁵ These accounts come from Mike Goldsmith's history Discord: The Story of Noise, as summarized by The Marginalian.

The Babbage fight set a pattern that runs through the rest of this history. The people bothered by a sound and the people making it often come from different classes and trades, and the argument over who gets to make noise is also an argument over whose work and whose rest count.

Bass's Act is formally 27 & 28 Vict. c. 55, "An Act for the better Regulation of Street Music within the Metropolitan Police District," passed on July 25, 1864; legislation.gov.uk files it as the Metropolitan Police Act 1864.⁸⁶ It let a householder require a street musician or singer to leave the neighborhood of the house because of illness in the household, interference with ordinary occupations, or another reasonable cause.⁸⁶

Julia Barnett Rice and the tugboat whistles (New York, 1906)

What you hear: a tugboat whistle on the river at 2 a.m., then another.

Julia Barnett Rice (1860-1929) began her campaign after a worker at Bellevue Hospital told her that tugboat horns made "patients imagine demons are after them."⁸⁷ Columbia students counted about 5,000 unnecessary tugboat horn blasts a night.⁸⁷ In 1906 she founded the Society for the Suppression of Unnecessary Noise,⁸⁸ and the next year the Bennett Act let steamboat inspectors regulate whistle use.⁸⁷

The Society also ran a children's branch that kept noise down near hospitals.⁸⁷ Its name made the argument for it: the target was not all noise, only noise nobody needed. That distinction between necessary and unnecessary sound still underlies many city noise codes, which tend to regulate how and when a sound is made rather than whether it may exist.

New York measures its noise (1929-1936)

What you hear: elevated trains, riveting, car horns and radios - the city of the late 1920s.

By the 1920s, people had instruments for measuring sound. NoiseOFF's timeline records Homer Clyde Snook making early instrument-based street measurements in New York in 1925.⁸⁸ In 1929 the city set up a Noise Abatement Commission, which began studying street noise using the decibel.⁸⁸ The Commission took instruments across the city and ran questionnaires in newspapers asking what kept people awake.⁸⁹

Its 1930 report, City Noise, ran 308 illustrated pages.⁸⁹ It proposed reducing noise at its source and amending the city's sanitary code.⁸⁸ By CityRealty's account, the report "would ultimately have little impact."⁸⁹ The push did continue: in 1935 Mayor Fiorello La Guardia promoted "noiseless nights," drawing about 20,000 letters, and in 1936 New York adopted its first comprehensive noise code.⁸⁸

The lasting change was the method. Measuring street sound in decibels, and asking residents what bothered them, are still the two halves of how cities study noise. NoiseOFF is a noise-reduction advocacy group, so its timeline is a starting point rather than the last word.

The Commission was appointed by Health Commissioner Dr. Shirley W. Wynne, and the library record for City Noise lists Lewis H. Brown as chairman.⁹⁰ About 11,000 New Yorkers returned the questionnaire; according to The Spectator's December 1930 review, motor traffic topped the complaints at 36 percent, the subway, elevated and streetcars came second at 16 percent, and radios third at 12 percent.⁹¹

The US Noise Control Act of 1972 and the office that vanished

What you hear: nothing at the federal level, which is the story.

The Noise Control Act of 1972 directed the US Environmental Protection Agency to regulate noise from products sold across state lines, from railroads and from interstate trucks, and to handle labeling, federal purchasing, coordination and research.⁵⁹ EPA set up the Office of Noise Abatement and Control (ONAC) to do the work.⁸⁸ The Quiet Communities Act of 1978 added grants and technical help for state and local noise programs.⁵⁹

The Act also preempted state and local emission standards for products EPA regulated, while leaving states and cities free to set rules on how and when things are used or operated.⁵⁹ That split still shapes local noise law (see who makes the noise rules): a city generally regulates when a leaf blower may run, not how loud the factory may build it.

In early 1981, the Office of Management and Budget decided to end ONAC's funding and Congress went along.⁵⁹ EPA noise staff went from 175 to zero; an NIH panel dated the office's elimination to 1982.⁵⁹ The Act was never repealed, so on paper EPA remains responsible for noise with no budget to act on it. Sidney Shapiro's November 1991 report on it for the Administrative Conference of the United States is titled The Dormant Noise Control Act and Options to Abate Noise Pollution.⁵⁹ Noise control fell mainly to states and cities.⁸⁸

Boston's local layer was built in the same years. Most of the city's current noise ordinance, City Code 16-26, was enacted between 1984 and 1991 and amended through 2008.⁶² Its Air Pollution Control Commission adopted separate noise regulations under state law (General Laws chapter 40, section 21) and the city code, citing the Noise Control Act of 1972 and including clauses that would adopt future EPA noise standards automatically.⁹² How those two layers work today is covered in the sound of Boston.

Europe maps its noise: the 2002 Directive

What you hear: the same traffic as anywhere - but someone is required to count who hears it.

The EU's Environmental Noise Directive (2002/49/EC) was published in the Official Journal on 18 July 2002.¹² It required member states to produce strategic noise maps for large urban areas and for major roads, railways and airports. The first round, due 30 June 2007, covered agglomerations over 250,000 people, roads with more than 6 million vehicles a year, railways with more than 60,000 trains a year and airports with more than 50,000 movements; the second round, due 30 June 2012, lowered the thresholds to agglomerations over 100,000, roads over 3 million vehicles and railways over 30,000 trains. Maps are reviewed every five years.¹²

The Directive standardized the yardsticks - Lday, Levening, Lnight and Lden - but deliberately set no EU-wide limits.¹² Its action plans must reduce noise where needed, preserve areas of good acoustic quality, and inform and consult the public.²⁵ Each country chooses its own limits.

Set side by side, the two approaches split around the same years. The US built a federal regulator in 1972 and unfunded it a decade later; the EU, thirty years on, chose to measure and report everywhere and leave the limits national.

From noise to soundscape: Schafer and ISO 12913

What you hear: a church bell, a foghorn, birds in a park - the sounds a place would be poorer without.

In 1969, Michael Southworth, then a city-planning PhD student at MIT, published "The sonic environment of cities" in the journal Environment and Behavior, the first scientific use of the word soundscape.⁹³ In 1972, Canadian composer R. Murray Schafer began the World Soundscape Project at Simon Fraser University with a study of Vancouver.⁹³ The project grew out of Schafer's course on noise pollution, and its members included Hildegard Westerkamp, Barry Truax, Howard Broomfield, Peter Huse and Bruce Davis.⁹⁴

Its output included The Vancouver Soundscape (1973), Five Village Soundscapes, a European Sound Diary from a 1975 trip, Schafer's book The Tuning of the World (1977) and Truax's Handbook for Acoustic Ecology (1978).⁹⁴ The shift was from treating sound only as a pollutant to be reduced toward studying the whole sound environment of a place, including what is worth protecting.

The idea eventually became a standard. ISO 12913-1 (2014) defines soundscape as the "acoustic environment as perceived or experienced and/or understood by a person or people, in context," and ISO/TS 12913-2 (2018) covers how to collect and report soundscape data, with a third part on analysis.⁹³ The soundscape approach turns up in European research and some city plans, while in the US it is not a regulatory standard. The EU Directive's requirement to protect "areas of good acoustic quality"²⁵ is the closest the law has come to the same thought. Where to find that kind of quiet today is covered in measuring, mapping and finding quiet.

The noise log

The dates behind this guide, from Caesar's wagon rule onward, on one scrollable line.

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06Sirens, horns and alarms

The short version: A modern emergency siren is a speaker playing a menu of synthesized tones - wail, yelp, hi-lo, phaser - chosen by the driver for the traffic in front of them. How loud it is depends on where you stand: a 1985 federal field study measured an ambulance siren at 122 dBA at 10 feet and 98-105 dBA at 100 feet. Countries do not agree on what a siren should sound like - German law allows a single two-tone horn as the warning tone - and fixed outdoor sirens, Japan's evening chimes and car alarms each follow their own rules.

What are the different siren sounds?

What you hear: a slow rise and fall, then a frantic fast warble as the vehicle reaches an intersection, sometimes two alternating notes or a blast of air horn.

Electronic sirens synthesize their tones and play them through external speakers mounted on the roof or behind the grille. The standard menu includes wail, yelp, pierce/priority/phaser, hi-lo, scan, air horn and a manual mode⁹⁵. Older mechanical sirens make the wail physically: a rotor spins up and slows down, and the pitch rises and falls with it. A mechanical hi-lo uses solenoids to switch air between two rows of ports⁹⁵.

Two-tone sirens often sound a minor third apart; some police sirens use a tritone⁹⁵.

The history runs from bells to a two-tone (duotone) air horn in the 1970s, which the electronic wail overtook in the 1980s, according to Wikipedia's account, which does not name the country but reads as US history⁹⁵. Some US fire apparatus still carry a mechanical siren, the Federal Signal Q2B, rated at 123 dB at 10 feet (weighting not stated)⁹⁵.

What is the police siren that makes my car shake?

What you hear: a deep, throbbing pulse under the regular siren, often felt through the floor or steering wheel before you notice it as a sound.

That is probably a Rumbler, a Federal Signal add-on developed in 2007 and tested by the New York Police Department that year as an "intersection clearing device"⁹⁶. It plays a low-frequency tone between 182 and 400 Hz alongside the standard siren⁹⁶. The manufacturer says the unit senses the primary siren tone and drops its frequency by 75%, claims "up to 10 dB more sound pressure inside civilian vehicles," and limits each activation to eight seconds before it shuts off automatically; it is rated at 80 W⁹⁷. Those performance figures are the maker's own claims.

By 2012 more than 100 US police departments had deployed it, according to the advocacy group Noise Off as reported by Wikipedia⁹⁶. The manufacturer's own product page warns that audible equipment can cause hearing damage and recommends hearing protection⁹⁷.

The logic is physics. Drivers in sealed, insulated cars with music on often miss a siren, and low frequencies pass through car bodies better than high ones. The Rumbler trades a sound you hear for a vibration you feel.

Why do sirens sound different in Europe?

What you hear: in a German city, a steady "ta-tu-ta-ta" alternating between two notes, with none of the American wail or yelp.

Because the law says so. In Germany, priority vehicles may use one emergency tone: the two-tone Martinshorn (formally the Folgetonhorn or Einsatzhorn), defined by the standard DIN 14610⁹⁸. The current edition of DIN 14610, "Sound warning devices for authorized emergency vehicles," is dated March 2022⁹⁹; a petitioner to the German parliament said the standard's origins go back to 1935⁹⁸. Emergency horns must also meet Technical Requirement No. 32, which references DIN 14610⁹⁸.

In 2022 that petition asked the Bundestag to allow US-style wail and yelp. The government's position, as summarized in the closing statement, cited a Federal Highway Research Institute (BASt) study that found no basis for changing the signals and said how far a siren carries depends mainly on the traffic situation⁹⁸. The petition was closed on March 14, 2024 as "partially met": yelp was introduced, but only as a stop signal for police and customs vehicles under section 55(3a) of the vehicle licensing regulations (StVZO), not as a general warning tone⁹⁸.

In the US, by contrast, an emergency vehicle can rotate through the full electronic menu described above⁹⁵. German-style pneumatic two-tone (hi-lo) units switch between a high and a low air horn and can reach about 125 dB, depending on the compressor and horns (distance not stated)⁹⁵.

In the UK, the two-tone horn behind the "nee-naw" goes back at least to the 1960s: the British Red Cross museum holds a set of Fiamm two-tone air horns, made between 1960 and 1970, that were fitted to an ambulance as its siren¹⁰⁰. UK law still names the device. The Road Vehicles (Construction and Use) Regulations 1986 bar any motor vehicle from being fitted with a bell, gong, siren or two-tone horn, with exceptions for fire, police and ambulance vehicles and a list of rescue and other services¹⁰¹.

How loud is an ambulance siren?

What you hear: painful at the curb, still loud a block away.

The best-documented US figure comes from a 1985 National Institute for Occupational Safety and Health (NIOSH) Health Hazard Evaluation, requested by the General Services Administration before it revised the federal ambulance specification. Outside the vehicle, NIOSH measured 122 dBA at 10 feet (3 m) and 98-105 dBA at 100 feet (30 m)¹⁰². That is where the commonly quoted "about 120 dB at 10 feet" comes from.

The crew hears it too. With roof-mounted speakers, NIOSH measured 109 dBA at the driver and 91 dBA at the patient. Moving the speakers to the grille cut that to 87 dBA at the driver and 76 dBA at the patient¹⁰². NIOSH recommended grille or bumper speakers, closed windows, and using the siren only when necessary¹⁰². A 2007 study found passenger compartment levels could still exceed 90 dBA⁹⁵. For reference, the same NIOSH report cites the OSHA permissible exposure limit of 90 dBA as an 8-hour time-weighted average¹⁰² - a workplace limit, not a figure to compare directly with a single siren pass.

Speaker count matters: dual-speaker electronic systems average about 3 dB more than single-speaker systems⁹⁵.

Who sets the siren standards?

In the US, SAE J1849, "Emergency Vehicle Sirens," is the recommended practice for laboratory test procedures, requirements and guidelines for single-speaker electronic and electromechanical sirens on authorized emergency vehicles. SAE issued it in July 1989, stabilized it in October 2012 and revised it in February 2020¹⁰³. The federal ambulance specification, KKK-A-1822, is issued by the General Services Administration - the agency that requested the 1985 NIOSH study¹⁰².

The 2007 edition, KKK-A-1822F, requires a combination electronic siren and public address system "capable of producing a continuous warning sound at a minimum level of 123 dB, A-weighted, at 10'," with dual speakers mounted outside the vehicle in the bumper or hood area¹⁰⁴. That is a floor, not a ceiling, and the bumper placement matches what NIOSH recommended in 1985¹⁰².

Elsewhere, standards follow local choices. Singapore's Ministry of Home Affairs told parliament on January 12, 2026 that its emergency vehicle sirens "meet the SAE J1849 international standard"¹⁰⁵. Germany uses DIN 14610⁹⁹.

Why can't I tell which direction a siren is coming from?

What you hear: a siren that seems to come from everywhere at once, then appears from the street you weren't watching.

Your brain locates sound with three cues: the difference in arrival time between your two ears, the difference in level between them, and the way your outer ear filters sound depending on its direction (the head-related transfer function). All three work best on broadband sound, which spreads energy over many frequencies⁹⁵.

A classic siren is close to the opposite: a fairly pure tone sweeping through a narrow band. Sirens also use relatively low frequencies on purpose, because low sound bends around corners and through openings better⁹⁵. That helps a siren reach you, but not tell you where it is. In a city, the sound also bounces off building faces (see what hard walls and tall buildings do), so the timing and level cues arrive scrambled. Treat that last point as a reasoned explanation rather than a measured result.

The broadband idea has made it into backup alarms: OSHA told a manufacturer in 2004 that a "white noise" backup alarm can comply with construction rules as long as it warns workers in time¹⁰⁶. The full story is in construction, backup beepers and leaf blowers.

What are outdoor warning sirens, and why do they test them?

What you hear: a long, steady tone from a pole-mounted siren, usually at the same time on a set day; or, in a Japanese town, a gentle melody at dusk.

Fixed outdoor sirens warn of disasters or attack. The traditional civil defense code used a steady tone for an alert and a wavering wail for attack; many towns also tested fire sirens daily at noon, and many communities switched fire sirens off after pagers arrived in the 1970s⁹⁵.

Hawaii sounds its statewide outdoor warning sirens on a schedule. The test on Friday, May 1, 2026 sounded at 11:45 a.m. as a one-minute steady "Attention Alert Signal," paired with a test of the Emergency Alert System live audio broadcast¹⁰⁷.

The Hawaii Emergency Management Agency runs the siren test monthly, together with an Emergency Alert System test, "normally on the first working day of the month," at 11:45 a.m., with a one-minute steady tone, per a 2017 agency advisory¹⁰⁸. Its July 2024 release followed the same pattern - Monday, July 1, at 11:45 a.m., a one-minute steady "Attention Alert Signal" - and asked the public to report siren problems to county civil defense agencies¹⁰⁹.

Japan does it with music. The tune you hear at the end of the day in most Japanese towns is a test of bosai musen ("disaster wireless"), the municipal loudspeaker network, nicknamed goji no chaimu, the 5 p.m. bell. More than 90% of municipalities have one. The test plays at 5 p.m. in winter and moves to 5:30 or 6 p.m. as days lengthen, using one of 32 standard tunes, with "Yuyake Koyake" a favorite. The national system was launched after the 1964 Niigata earthquake and is linked to J-Alert, introduced in 2007¹¹⁰.

The chime doubles as a signal for children to head home¹¹⁰. "Yuyake Koyake" began as a 1919 poem by Uko Nakamura and was set to music about five years later; some Tokyo wards have their own chimes, and one, Bunkyo-ku, has none, according to Metropolis¹¹¹. Japan's other designed melodies, at stations and crossings, are in sounds made on purpose.

Do car alarms actually stop theft?

What you hear: a cycling pattern of whoops, honks and chirps from a parked car, usually with nobody coming to check.

The evidence collected by critics says mostly no. A March 2003 report by the advocacy group Transportation Alternatives, "Alarmingly Useless," cited authorities' estimates that 95% to 99% of car alarms are false. It also cited a 1997 Highway Loss Data Institute analysis of 73 million vehicles that found alarm-equipped cars "show no overall reduction in theft losses"¹¹². The same report said noise made up 83% of 97,000 calls to the New York Police Department's Quality of Life Hotline in 2001, with car alarms near the top, and estimated the cost of car alarm noise in New York City at $400-500 million a year¹¹². Those cost figures are an advocacy estimate.

The politics were not one-sided. In 2003, New York City Councilwoman Eva Moskowitz introduced a bill to outlaw car alarms, with fines of up to $2,100 for frequent offenders; the city's Department of Environmental Protection and the NYPD testified against a ban¹¹³.

The bill that became law came from Councilmember John Liu. Int. 81-A made it illegal to sell an audible car alarm that does not shut itself off within three minutes or that can be set off without anyone touching the car, and barred anyone other than a manufacturer from installing one. Mayor Michael Bloomberg vetoed it on August 16, 2004, and the Council overrode the veto on September 28, 2004, enacting it as Local Law 43 of 2004. As enacted, fines run from $500-1,000 for a first violation to $2,500-5,000 for a third or later, enforced by the NYPD and the Department of Consumer Affairs¹¹⁴.

In Boston

Boston's city code limits car alarms: an alarm that is plainly audible 200 feet away must shut itself off automatically within five minutes, with a $50 fine, according to a 2016 printout of the noise chapter (16-26)⁶². The same chapter exempts noise from emergency vehicles during an actual emergency⁶². The city routes car alarm complaints to the Boston Police¹¹⁵.

Elsewhere in the world

• Germany: one legal emergency tone, the DIN 14610 two-tone horn; yelp allowed since 2024 only as a police and customs stop signal⁹⁸.
• Singapore: emergency vehicle sirens meet SAE J1849, per the Ministry of Home Affairs (January 2026)¹⁰⁵.
• Japan: daily melodic tests of the bosai musen disaster speakers, in more than 90% of municipalities¹¹⁰.
• United States: multiple electronic tones, SAE J1849 testing, and in some police fleets the low-frequency Rumbler¹¹⁶⁹⁶.

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07Traffic: tires, engines, horns and noise cameras

The short version: Road traffic is the noise source that reaches the most people. In Europe, about 100 million people lived with road noise at or above 55 dB Lden in 2012, five times the count for railways. Above about 20 mph (32 km/h), most of what you hear from a passing car is its tires on the pavement, not its engine, which is why speed and road surface matter as much as mufflers. The loudest single vehicles - modified exhausts, motorcycles, trucks using engine brakes - are the target of federal limits, local ordinances and a new and disputed tool, the noise camera.

Is traffic really the biggest source of city noise?

What you hear: A steady wash of sound that never quite stops, louder at rush hour, with trucks standing out above the cars.

In Europe, yes, by a wide margin. The European Environment Agency (EEA) counted about 100 million people in its 33 member countries exposed to road traffic noise at or above 55 dB Lden in 2012, and 32 million above 65 dB Lden.¹¹⁷ Railways came second at 19 million people above 55 dB Lden, aircraft third at more than 4.1 million, and industry in urban areas at about 1.0 million.¹¹⁷ Those figures come from a 2017 EEA briefing with 2012 as the reference year, and the advocacy group Transport & Environment reported the same numbers in May 2017.¹¹⁸ The EEA's 2025 report, using 2022 data, put road noise at about 92 million people at or above 55 dB Lden, rail at about 18 million and aircraft at about 2.6 million.²

Lden (day-evening-night level) is a 24-hour average that adds a penalty to evening and night sound, because the same noise bothers people more after dark. It is the metric the EU uses to map road, rail and aircraft noise; sound and decibels explains how it differs from US metrics. The US does not publish a comparable national exposure count for all roads; its federal highway rules use hourly levels instead (see the noise wall section below).

The EEA briefing reports that the World Health Organization ranks road traffic noise as the second most harmful environmental stressor in Europe, after air pollution, with effects including sleep disturbance, cardiovascular disease, hypertension, cognitive impairment and annoyance.¹¹⁷ What the studies behind those effects show is covered in the health section.

The closest US figure covers Interstates only. The Bureau of Transportation Statistics' National Transportation Noise Map, released March 21, 2017 with 2014 data, estimated that 98.00% of the US population was potentially exposed to Interstate highway noise below 50 dBA (24-hour LAeq), 0.25% to 70 to 79 dBA and 0.06% to 80 dBA or more.²³ BTS describes the model as a worst case, with no shielding from buildings or terrain, so these are potential exposures, not measurements.²³

Why doesn't cutting traffic in half make it twice as quiet?

What you hear: A road with half the cars sounds only a little calmer.

Decibels are logarithmic, so sound energy and perceived loudness do not track each other the way intuition expects. According to a US concrete-pavement research center, halving traffic volume lowers the sound level by only about 3 dBA.¹¹⁹ A change of 1 to 3 dB is hard to notice, 5 dB is noticeable to most people, and a 10 dB drop is judged to be about half as loud.¹¹⁹

The same brief gives three other rules of thumb. A truck is about 8 dBA louder than a car. Roadway sound drops about 3 to 5 dB for each doubling of distance from the road. And each 10 mph increase in speed raises the level by about 2 to 3 dBA.¹¹⁹ By those rules of thumb, slowing traffic or taking trucks off a road can do more than removing a share of the cars.

Are tires or engines louder?

What you hear: At low speed, an engine note and the clatter of an exhaust. On the highway, a roar or whine that seems to come from the road itself.

For cars at steady speed, tire-pavement noise - sound made where the tread meets the road - becomes the main source above about 20 mph (about 32 km/h). For trucks, that crossover speed is higher.¹¹⁹ Below the crossover, the engine, intake and exhaust dominate. Above it, a quieter engine makes little difference, and the road surface and tire tread take over.

The most influential pavement factor is "positive texture": small bumps protruding above the surface that the tire strikes as it rolls. Quieter surfaces have a very fine, "negative" texture, with voids and grooves below the surface rather than bumps above it.¹¹⁹

Engineers measure this with microphones mounted a few inches from a test tire as it rolls. In the US the usual method is OBSI (on-board sound intensity); elsewhere a related method called CPX (close-proximity) is more common.¹¹⁹

This is also why electric vehicles are not much quieter at highway speed: above the crossover, the tires are the noise. The artificial sounds electric cars must play at low speed are covered in sounds made on purpose.

What is quiet pavement, and does it last?

What you hear: The roar drops noticeably when you drive from one stretch of highway onto a newer, darker or grooved one.

Several surfaces can cut tire noise, but the numbers vary widely from study to study. A March 2025 literature review for the California Department of Transportation (Caltrans) collected these results:¹²⁰

Open-graded friction course (OGFC) is a porous asphalt with connected air voids that absorb some of the noise made at the tire. Durability is the catch. Arizona's rubberized overlay lost about 2 dB of its benefit over four years, and an experimental section in Washington State lost nearly all of its benefit in just over two years.¹²⁰

Arizona's Department of Transportation started a Quiet Pavement Pilot Program in April 2003, working with the Federal Highway Administration (FHWA) and the Volpe Center.¹²⁰ As of the Caltrans review in March 2025, quieter pavement was still not an FHWA-approved noise abatement measure for federal projects, although a proposed change to the federal rule hinted it might become one.¹²⁰

The proposal in question is FHWA's overhaul of 23 CFR Part 772, published on October 18, 2024, with comments due December 17, 2024. Among other changes, it would lower the Table 1 impact levels by 1 dB(A) and apply Type I project requirements to federally funded abatement on existing roads, which it says include "changing the pavement surface or building noise barriers."¹²¹ As of October 2026, a search of the Federal Register found no final rule, so the 2010 rule and its table below still apply.¹²²

When does a highway get a noise wall?

What you hear: Traffic noise that suddenly softens when a concrete or wooden wall appears between the road and the houses.

In the US, federally funded highway projects follow a rule at 23 CFR Part 772. When predicted noise at a nearby property "approaches" or exceeds the Noise Abatement Criteria (NAC), the state has to consider abatement, usually a wall. The criteria are written in Leq(h), the steady level that carries the same sound energy as the actual fluctuating traffic over one hour. The table below is the federal Table 1, as reproduced in New Hampshire's 2016 noise policy:¹²³

"Approach" means within 1 dBA below the criterion, so a home predicted at 66 dBA Leq(h) counts.¹²³ States also flag a "substantial increase" over existing levels; New Hampshire defines that as 15 dBA or more.¹²³

Considering a wall is not the same as getting one. A barrier is not "feasible" unless it cuts at least 5 dBA for at least one impacted home. Then it has to be "reasonable," which each state defines within the federal rule. New Hampshire requires at least 7 dBA at one benefited home, aims for 10 dBA or more at first-row homes, and starts its cost test from a base of 1,500 square feet of wall per benefited home, adjusted by policy factors.¹²³

Insertion loss is the number of decibels a wall takes off compared with no wall. For homes directly behind a barrier, the CP Tech Center brief puts it at about 5 to 10 dBA, and says effectiveness falls off beyond about 300 to 500 feet (90 to 150 m) from the road.¹¹⁹ By the perception rule above, 10 dBA is roughly half as loud. People several blocks back often notice little change.

In Massachusetts, MassDOT says it uses the federal Type I noise abatement program under 23 CFR 772 and approves a barrier when "enough people will receive a high enough benefit for the cost." Its page lists no request process for residents; it points questions to MassDOT's online contact form.¹²⁴ Some existing walls came from the former Massachusetts Turnpike Authority's Type II (retrofit) program, and a 2026 MassDOT FAQ on new barriers in Allston says state policy included a formal vote by residents on whether to advance a barrier.¹²⁵

Is it illegal to honk for no reason?

What you hear: Short taps at a green light, long blasts in gridlock, a car alarm's cousin at 2am.

In the US, horn rules are set mainly by state law. North Carolina's is typical in shape: a vehicle must have a horn "capable of emitting sound audible under normal conditions from a distance of not less than 200 feet," the driver may use it only as a reasonable warning, and the horn may not emit an "unnecessary or unreasonable loud or harsh sound."¹²⁶ So a horn has a minimum audibility, and its use is limited to warning, but the statute sets no decibel cap.

In Massachusetts, General Laws chapter 90, section 7 requires a motor vehicle to carry "a suitable bell, horn or other means of signalling."¹²⁷ Section 16 provides that "No person operating a motor vehicle shall sound a bell, horn or other device, nor in any manner operate such motor vehicle so as to make a harsh, objectionable or unreasonable noise."¹²⁸ Neither section sets a decibel limit for horns.¹²⁸

Elsewhere in the world: horns in India

What you hear: A near-continuous layer of honking at every intersection.

India is a frequently cited case study for horn culture. NPR reported in September 2025 that a 2019 study found average noise in Mumbai often above 80 decibels, and counted 27 honks in one minute at a single intersection.¹²⁹ Sumaira Abdulali of the Awaaz Foundation, a Mumbai activist, told NPR that horns reach about 120 decibels; that is her estimate, and no weighting or distance was given.¹²⁹ Fines run up to about $25.¹²⁹ Road minister Nitin Gadkari proposed replacing horn sounds with Indian classical instruments; Abdulali called the idea a disaster.¹²⁹

In February 2020, Mumbai Police ran a "punishing signal": decibel meters at traffic lights reset the red-light countdown whenever honking at the intersection exceeded 85 dB, so the drivers who honked waited longer.¹³⁰

What are the rules on loud motorcycles and exhausts?

What you hear: A crackling, popping exhaust that sets off car alarms, or a motorcycle you can hear for blocks.

In the US, the Environmental Protection Agency (EPA) sets noise limits for new street motorcycles under 40 CFR 205.166: 83 dBA for model year 1983 and 80 dBA for 1986 and later, with moped-type motorcycles at 70 dBA. The exhaust must keep meeting the standard for one year or 6,000 km.¹³¹ Those numbers come from the federal test procedure and do not translate directly to a roadside reading.

Motorcycles built after December 31, 1982 carry a label on the chassis and a label on the muffler with matching codes. According to the advocacy site NoiseOFF, an unlabeled or non-matching exhaust on a regulated motorcycle violates section 4909(a)(2) of the federal Noise Control Act.¹³² Federal law makes tampering a violation, but enforcement in practice falls mostly to states and cities (see who makes the noise rules).

California's exhaust limits, as listed by the California Highway Patrol (CHP), are among the most specific: 95 dBA for passenger vehicles under 6,000 lb under an SAE stationary test (Vehicle Code 27151), 80 dBA for motorcycles (VC 27202), and 80 dBA for pickups from 6,001 to 10,000 lb and commercial vehicles (VC 27204).¹³³

How do noise cameras work, and do they hold up?

What you hear: Nothing different. A noise camera is a roadside sound meter wired to a license plate camera; when a passing vehicle crosses a set level, it records the plate and the sound.

The idea is contested. Supporters point to deterrence and relief for residents on streets used for late-night revving. Skeptics, including the California Highway Patrol, question whether the devices can reliably pick out the right vehicle. Where each program stands:

New York City. The Department of Environmental Protection (DEP) piloted noise cameras from June 2021. The meter triggers at 85 decibels or more, measured from at least 50 feet; the DEP letter does not state the weighting. As of August 2023, fines were $800 for a first offense, $1,700 for a second and $2,500 after that.¹³⁴ In December 2023 the City Council approved the "Stop Spreading the Noise Act," allowing the devices in all five boroughs.¹³³

California. SB 1079, by Senator Anthony Portantino, was signed on September 19, 2022 (Chapter 449). It added Vehicle Code 27150.4 and told the CHP to evaluate sound-activated enforcement devices and report by January 1, 2025.¹³³ In the CHP's trial, one vendor's system logged 328 events between February 9 and March 27, 2024, with exhaust noise from 72.7 to 115.3 dBA; a second vendor's interface was unsuitable, and a third produced no data. The CHP does not recommend the devices as a standalone basis for citations.¹³³

The same report notes that Knoxville, Tennessee tested a device from 2022 without issuing citations, and that Edmonton, Alberta ran a pilot from 2016 to 2020 before returning to traditional enforcement.¹³³

France. Bruitparif, the Paris-region noise observatory, built the Hydre noise radar from two of its Méduse sensors, each with four microphones; Méduse units had been deployed since summer 2019. The legal trial began on January 4, 2022, under the 2019 mobility law (LOM, article 92) and Decree 2022-1. Readings are normalized to 7.6 m, and one scooter measured 92.7 dB(A). The planned fine was 135 euros, reduced to 90 euros if paid within 15 days.¹³⁵

Pilot sites included Paris, Nice, Toulouse, Bron, Rueil-Malmaison, Villeneuve-le-Roi and the Haute Vallée de Chevreuse. A second phase with fines, initially planned for spring 2025, depends on type approval from LNE, the national metrology lab; a parliamentary question dated June 10, 2025 said no fines had yet been issued.¹³⁶

United Kingdom. The Department for Transport (DfT) ran a roadside trial from October 18, 2022 to February 1, 2023 in Keighley, Bristol and South Gloucestershire, Great Yarmouth and Rubery in Birmingham, with 300,000 pounds of funding. The reports were published on March 17, 2024.¹³⁷ According to the Institute of Acoustics, the cameras activated 1,777 times, and 4% of activations were attributed to excessively noisy vehicles. The proposed threshold is 95 dB LAmax at 7.5 m on roads with limits of 50 mph or less; a deterrent effect was observed, and the DfT planned to issue guidance to councils.¹³⁸ LAmax is the highest A-weighted level during the event.

The trigger levels are not comparable across programs: New York's is measured from at least 50 feet (about 15 m) with no weighting stated, the UK proposal is an LAmax at 7.5 m, and France normalizes to 7.6 m.

As of July 2026, the French motoring site Motorsactu reported that no noise radar fines had been issued; metrological testing for type approval began in late 2025, and approval was expected during 2026.¹³⁹ In New York City, DEP's annual report for calendar year 2025 says its cameras recorded 15,994 events and led to 1,691 summonses, with $1,472,265 in penalties imposed and $308,229 collected. The report does not state the trigger level, weighting or distance.¹⁴⁰

What does a "no engine brake" sign mean?

What you hear: A loud, rapid machine-gun rattle from a big truck slowing on a hill or approaching a town.

An engine compression brake, often called a "Jake brake" after one manufacturer, changes the exhaust valve timing so the engine absorbs power and slows the truck without wearing the wheel brakes. A legal note published by the Maine Department of Transportation says the brake is "quite loud" on trucks with poorly muffled or straight-pipe exhausts, and argues that the real problem is often defective or modified mufflers rather than the brake itself.¹⁴¹

In the US, according to the same note, federal rules require trucks to emit less than 80 dBA at 50 feet on a drive-by.¹⁴¹ Many towns post "no engine brake" signs, but the Maine note points out that a sign without an enforceable ordinance behind it is advisory only. It adds that federal law (42 U.S.C. 4917) can preempt local noise rules for interstate carriers unless the local rule matches federal standards, and that bans raise safety concerns on steep downgrades, where the engine brake keeps wheel brakes from overheating.¹⁴¹

Are electric garbage trucks quieter?

What you hear: The early-morning sequence of diesel idle, hydraulic whine, crash of a bin and the grind of the compactor.

Reports say yes for the driving part, less so for the compacting part. The reports below give no decibel figures. New York City's Department of Sanitation piloted a Mack LR Electric refuse truck from November 2020; it was described as "near-zero" noise, with added white noise so people know it is nearby.¹⁴² Copenhagen's Amager Resource Center received 86 electric Scania refuse trucks, and drivers reported much lower noise in the cab.¹⁴³

The most specific study comes from Finland. Tests by the research center VTT in autumn 2022 found an electric refuse truck "notably quieter" than a diesel one, but the noise of compacting the trash was unchanged. Adding a rubber mat in the hopper and an enclosure around the hydraulic pump cut handling noise.¹⁴⁴ An electric drivetrain removes the engine idle; the bang of bins and the crush of the load are a separate engineering problem.

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08Trains, subways and the screech on the curve

The short version: In the US, a federal rule requires locomotive horns at public grade crossings, at 96 to 110 dB(A) measured 100 feet ahead of the locomotive, in a long-long-short-long pattern, and the only way to silence them is a quiet zone backed by extra safety measures. Underground, the loudest sound is often wheel squeal on tight curves, which can reach about 100 dB(A) at 10 m; New York City studies have recorded subway platform peaks of 102 to 106 dBA. Lubrication, water spray and other fixes help at some sites and not at others.

How loud is a train horn, and why do trains honk at night?

What you hear: Two long blasts, a short one and a final long one, held until the train reaches the crossing, at any hour.

The Federal Railroad Administration (FRA) Train Horn Rule, at 49 CFR Part 222, requires locomotive engineers to begin sounding the horn 15 to 20 seconds before reaching a public grade crossing, and for fast trains no more than a quarter mile ahead. The pattern is two long, one short and one long, repeated or prolonged until the locomotive occupies the crossing.¹⁴⁵ The rule does not change at night, which is why horns are often most noticeable then: the horn is the same, but the background is quieter.

The horn must be at least 96 dB(A) and no more than 110 dB(A), measured 100 feet ahead as described below. The final rule moved the measurement microphone to 15 feet above the top of the rail, up from 4 feet.¹⁴⁶

Dates for the rule are often given inconsistently. FRA published the final rule on April 27, 2005 (70 FR 21844), and it took effect June 24, 2005.¹⁴⁶¹⁴⁷ FRA then amended it in a final rule responding to petitions for reconsideration, published August 17, 2006 (71 FR 47614) and effective September 18, 2006.¹⁴⁷ FRA's current web page describes the rule as "effective August 17, 2006," which is the publication date of those amendments, not their effective date.¹⁴⁵¹⁴⁷

Under 49 CFR 229.129, the 96 to 110 dB(A) range applies at 100 feet forward of the locomotive in its direction of travel, with the test microphone 15 feet above the top of the rail for standard horns and 4 feet for cab-mounted or low-mounted horns.¹⁴⁸

How does a town get a train quiet zone?

What you hear: Trains rolling through crossings with bells and gates but no horn.

A quiet zone is a stretch of line where trains do not routinely sound horns at crossings. Only a public authority that controls the crossings - typically a city or town - can create one; a railroad or a group of neighbors cannot.¹⁴⁵ The authority has to add safety measures that make up for the lost warning, and a quiet zone is generally at least half a mile long.¹⁴⁶ Whistle bans that existed before the rule could be grandfathered under certain conditions.¹⁴⁶

An alternative is a wayside horn: a horn mounted at a gated crossing and aimed down the road at drivers, which can substitute for the train horn and covers a much smaller area.¹⁴⁶ Even inside a quiet zone, engineers may still sound the horn in an emergency, such as a person or vehicle on the tracks.¹⁴⁵

Nationally, the Government Accountability Office counted 570 new quiet zones - those established under the rule - in 42 states as of June 2017.¹⁴⁹

Other countries handle this differently. In Canada, the Canadian Rail Operating Rules require trains to whistle at every public grade crossing. A municipality can stop it by assessing the crossings with the railway against section 104 of the Grade Crossings Regulations, giving public notice and passing a council resolution; the railway then issues instructions to stop whistling and must confirm in writing within 30 days after it stops, and a Transport Canada inspector can order whistling to resume if the crossings are not maintained.¹⁵⁰

In Great Britain, drivers sound the horn at about 1,600 crossings marked with whistle boards. Network Rail's Night Time Quiet Period, introduced in 2007, limits horn use there to emergencies at night; in December 2016 it was shortened from 11 p.m.-7 a.m. to 11:59 p.m.-6 a.m., after a 2015 RSSB study found that 64% of near misses during the quiet period happened in its shoulder hours.¹⁵¹

How many people hear rail noise?

In Europe, the European Environment Agency counted 19 million people exposed to railway noise at or above 55 dB Lden in 2012, second only to road traffic at about 100 million (see traffic).¹¹⁷ Lden is a 24-hour average with penalties for evening and night sound. The EEA's 2025 report, using 2022 data, put the rail figure at about 18 million.²

How loud is the subway?

What you hear: A roar as the train enters the station, brake hiss, and on some lines a high shriek that makes people cover their ears.

Two New York City studies give the clearest numbers. A 2006 pilot survey by Robyn Gershon and colleagues, reported in the Journal of Urban Health, found an average maximum of 94 dBA on subway platforms, 95 dBA inside subway cars and 84 dBA at bus stops. The highest platform reading was 106 dBA, and more than 1 in 10 platform readings were above 100 dBA.¹⁵²

A 2009 study by Richard Neitzel and colleagues in the American Journal of Public Health measured an average of 80.4 dBA on the subway, the highest of the transit modes it measured (Metro-North commuter rail averaged 75.2 dBA). The maximum was 102.1 dBA on a platform, and about half of the subway maximum readings were above 90 dBA.¹⁵³ The University of Washington's write-up compared these with EPA and WHO guidance of 70 dBA averaged over 24 hours to protect hearing.¹⁵³

Keep the metrics apart: the 80.4 dBA figure is an average over a ride, while the 94, 102.1 and 106 dBA figures are maximums, the loudest moment of a reading. A brief peak and a long average describe different things and are not interchangeable. What those levels mean for hearing is covered in the health section.

For London, a 2015 paper in the Proceedings of the Institute of Acoustics by researchers at London South Bank University measured whole Underground journeys, including platform waits, walking and interchanges, with a shoulder-worn dosimeter. Journey averages ran from 84.3 to 85.5 dB LAeq, and a 12-minute seated stretch of the Central line averaged 90.9 dB LAeq. The highest C-weighted peak was 131.1 dB LCpeak, a peak metric that cannot be compared with the averages.¹⁵⁴ The paper cites earlier work finding platform levels often above 80 dB LAeq while a train arrived, boarded and left.¹⁵⁴

Why do trains screech on curves?

What you hear: A piercing, almost musical squeal as a train rounds a tight bend, sometimes rising and falling in pitch.

A rail vehicle's wheels are fixed to axles, so on a tight curve they cannot steer perfectly along the rail. The wheels slip sideways across the railhead, and that stick-slip motion makes the wheel ring like a bowed string. A 2005 report for the International Union of Railways (UIC) lists three mechanisms: lateral creep (the sideways slip, which it calls the most important), flange rubbing, and slip along the direction of travel. Squeal frequencies run up to 10,000 Hz, and levels reach about 100 dB(A) at 10 m.¹⁵⁵

Wheel squeal is separate from the general roar of a train, which comes from wheels rolling on rails and from the motors. The squeal is a tone, concentrated at a few high frequencies, and it is why the same train sounds fine on straight track and painful on one particular curve.

How bad a given curve is depends on its radius, the wheel and rail profiles, the climate and maintenance, so results from one site rarely transfer neatly to another.¹⁵⁵

What fixes wheel squeal?

What you hear: The same curve that shrieked last month is quieter now, or worse.

The UIC report reviewed trials across European railways, and the results were mixed:¹⁵⁵

L10, L20 and L50 are statistical levels: the level exceeded 10%, 20% or 50% of the time during the measurement. The table's numbers come from different sites and metrics, so they show which fixes worked where, not a ranking.

Rail grinding, which reshapes the railhead, is another maintenance option. Its best-documented effect is on rolling noise rather than squeal: after 2016 grinding campaigns on Dublin's Luas light rail, Transport Infrastructure Ireland measured pass-by reductions of 4.0 to 11.7 dB LAeq,Tp at two sites, and the larger gain shrank by about 1 dB a month as corrugation returned.¹⁵⁶ That study measured rolling noise, not curve squeal.

In Boston: the Green Line at Boylston

What you hear: An inbound Green Line train shrieking as it turns from under Boylston Street onto Tremont.

The inbound turn at Boylston station is the squeal spot Boston riders cite most. In a 2017 WBUR report, an engineer from the acoustics firm Acentech called it "one of the sharpest turns in North America." The MBTA then had 13 greaser units on the Green Line with six more coming, and was testing graphite flange-stick lubricators. The curve's radius cannot be widened, because the tunnel is too old to rebuild around it.¹⁵⁷ For how a city's rail system works more broadly, see How a City Works: transit.

The Green Line has been a test bed for this before. A 1982 US Department of Transportation noise test found that a light rail vehicle on resilient wheels was about 10 dB quieter inside the car than a PCC streetcar on solid steel wheels, and found no significant difference in wayside noise on straight track between the two resilient wheel designs tested.¹⁵⁸ The sound of Boston covers more of the city's noise.

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09Planes, helicopters and the flight path overhead

The short version: In the US, airport noise is officially judged by a yearly average called DNL, with 65 DNL as the line for "significant" impact - a threshold the FAA's own 2021 survey suggests understates annoyance, and which the FAA is reviewing but has not changed as of October 2026. Individual planes have to meet certification limits that have tightened in steps, and newer engines are quieter by design. The complaints that grew fastest in the 2010s came less from louder planes than from satellite-guided routes that put the same planes over the same streets every time. Abroad, many big airports run night curfews or quotas; at home, most large airports offer a public flight map where you can see what flew over and file a complaint.

How is airport noise measured in the US?

What you hear: individual planes. What the rules measure: a year of them averaged together.

The main US metric is DNL (Day-Night Average Sound Level), an annual average of A-weighted aircraft noise (weightings and averages are explained in Sound and decibels) at a location that adds a penalty for flights at night. ¹⁵⁹ Airports model DNL rather than measure it: for a federal noise study, contours must be produced with the FAA's Aviation Environmental Design Tool (AEDT), and data from noise monitors cannot be used to assess impacts. ¹⁵⁹

The night penalty is 10 dB: an FAA noise primer explains that DNL counts A-weighted sound between 10 p.m. and 7 a.m. as 10 dB louder than it really is. ⁶

Under the federal land-use guidance, everything below 65 DNL "is compatible with all uses." At or above 65 DNL, homes, schools, places of worship, hospitals, nursing homes and licensed daycares are listed as incompatible. ¹⁵⁹

Part 150 (14 CFR Part 150) is a voluntary program. An airport that does a Part 150 study must produce updated 65 DNL noise contours, a map of where the yearly average reaches that level. ¹⁵⁹ It can then propose a noise compatibility program - home and school sound insulation, limits on engine run-ups, "Fly Quiet" programs, voluntary purchase of homes - and the FAA reviews and approves the contours and measures. ¹⁵⁹ Approved measures become eligible for Airport Improvement Program grants covering 80% of the cost. ¹⁵⁹

So the answer to "can I get soundproofing from the airport?" usually runs through a Part 150 program and whether your home sits inside the approved contour.

There is an indoor test too. In FAA Compliance Guidance Letter 2022-03 (September 15, 2022), homes and schools inside the DNL 65 dBA contour are considered eligible for AIP-funded sound insulation, and eligible properties must have an interior noise level of DNL 45 dBA or above. ¹⁶⁰ Insulation is designed to bring habitable rooms down to that 45 dB DNL level, according to an earlier FAA program guidance letter (PGL 12-09, 2012, since canceled). ¹⁶¹

The criticism is about averaging: a yearly figure can stay the same while the number of loud single events, or the hours they happen, changes. That argument is part of the background to the FAA's current review, below.

What did the FAA's 2021 noise survey find, and is 65 DNL changing?

The Neighborhood Environmental Survey was the FAA's national study of how people near airports react to aircraft noise. Surveys went out by mail in six waves over 12 months starting October 2015, around 20 airports chosen from 95 candidates; 10,328 people responded by mail and about 2,000 also did a phone survey. ¹⁶²

Results were published in the Federal Register on January 13, 2021. ¹⁶² The new "National Curve" shows "a substantial increase in the percentage of people who are highly annoyed by aircraft noise" compared with the older Schultz Curve, including at lower noise levels. ¹⁶² Per a summary of the FAA study by Kaplan Kirsch, a law firm that represents both airports and airport communities, between 60.1% and 70.9% of people were highly annoyed at DNL 65 in 2016, versus 12.3% in the 1992 Schultz Curve data behind the current policy. ¹⁶³

On May 1, 2023, the FAA opened a formal Noise Policy Review covering whether DNL should stay the primary metric, whether 65 DNL should remain the significance threshold under the National Environmental Policy Act (NEPA), and what alternative or supplemental metrics might be used. ¹⁶⁴ The comment period ran to September 29, 2023 and drew 4,857 comments: 81% from individuals, 14% anonymous, 5% from organizations. ¹⁶⁴

Status as of October 2026: the FAA established an Aircraft Noise Advisory Committee (ANAC) on January 14, 2025, and on July 10, 2026 published a notice seeking members, with applications due August 10, 2026. ¹⁶⁴ The FAA says it "will complete the Noise Policy Review once the ANAC has submitted a report." ¹⁶⁴ No date for that report has been published. The 65 DNL threshold is under review, not changed.

What are aircraft noise "Stages" and ICAO "Chapters"?

Every new aircraft type has to meet a maximum noise level to be certified. In the US those limits live in 14 CFR Part 36 and are grouped into Stages; the FAA publishes certificated levels for each type in an advisory circular. ¹⁶⁵ The international equivalent is ICAO Annex 16, Volume I, grouped into Chapters. ¹⁶⁵

The US has also banned older, noisier stages from operating, in steps.

A short history explains the steps. The FAA's first noise standards, in 1969, covered new civil subsonic jet designs; in 1973 they were extended to newly produced aircraft; in 1976 the FAA set the 1985 phaseout of Stage 1 big jets; and in 1977 it introduced the "Stage" names and the stricter Stage 3. ¹⁶⁶ Certification limits apply to the type, so an older plane still flying is held to the stage it was built to.

Why are newer jets quieter?

What you hear: the older crackling roar at takeoff, versus a lower, smoother whoosh with a fan whine on approach.

Early jetliners used turbojets, which produce "high velocity hot exhaust jets during takeoff generating a great deal of noise." ¹⁶⁷ Most of that noise comes from turbulence where the fast exhaust mixes with the slower air around it. ¹⁶⁸

Turbofans put a large fan in front of the engine core and push much of the air around the core rather than through it. That "helped mitigate engine noise by reducing the jet exhaust velocity"; the more air bypassed, the slower and cooler the core jet. ¹⁶⁷ The share of air going around versus through is the bypass ratio; NASA researchers noted ratios approaching 9 in engines like the GE90. ¹⁶⁷

There is a trade-off in what you hear. In high-bypass engines "jet noise is becoming less and less of a contributor to total engine noise," and the big fan becomes a significant source, producing tones at the blade-passage frequency. ¹⁶⁸ That is part of why a modern jet on approach can sound more like a whine than a roar.

Manufacturers state the gains as smaller "noise footprints," and those claims are disputed. In 2012 Boeing's website said the 787's noise footprint was "60% smaller than those today of similarly sized planes," according to the UK's Aviation Environment Federation (AEF), a campaign group. ¹⁶⁹ AEF calculated that, if the footprint is drawn at 85 dB, a 60% smaller area works out to about a 3 dB drop in noise level, and called the improvement modest, adding that traffic growth was likely to erase it. ¹⁶⁹

Why are planes suddenly flying over my house?

What you hear: planes that used to be spread across the sky now pass over the same few blocks, one after another.

Starting in the 2010s, the FAA moved many airports onto satellite-guided RNAV (area navigation) procedures, part of its air traffic modernization program, NextGen. Older procedures left planes spread over a wide band; RNAV routes are flown very precisely, so the same track gets used flight after flight. The noise per plane may not change, but the people under the track hear far more of it. That shift drove lawsuits and local studies, with mixed results.

Phoenix. New departure routes at Sky Harbor took effect September 18, 2014, and the airport received more noise complaints in the next two weeks than in all of the prior year. ¹⁷⁰ On August 29, 2017, the US Court of Appeals for the D.C. Circuit held the FAA's approval "arbitrary and capricious," citing NEPA, the National Historic Preservation Act, Section 4(f) and FAA Order 1050.1E, vacated the order and sent it back to the FAA. ¹⁷⁰

Maryland. The state challenged new flight paths into Washington National (DCA) for lacking NEPA review. On March 10, 2020, the same court dismissed the case as untimely, finding "the state's delay of over 900 days was extreme." ¹⁷¹ The ruling turned on timing, not on whether the routes were properly reviewed.

Boston. The FAA released the environmental assessment for an RNAV departure from Logan's Runway 33L in May 2013, and new RNAV procedures began in 2014, concentrating 33L departures over parts of north and west Cambridge. ¹⁷² An FAA-funded study run by Massport and conducted by MIT looked at alternatives; in 2021 MIT proposed a modified route over central Somerville and Porter Square, which Cambridge and most of the communities on Massport's Community Advisory Committee voted against recommending. ¹⁷² Boston's flight paths are covered in more detail in The sound of Boston.

Does the airport have a curfew? (Elsewhere in the world)

Many large airports outside the US limit or ban night flights. The systems differ: some close outright, some cap the number of flights, some weight each flight by how loud the plane is.

Even with a cap, nights at Heathrow are not silent: about 80% of night flights land between 04:30 and 06:00, averaging 16 arrivals. ¹⁷³ The Frankfurt details here come from a Wikipedia summary rather than from the airport operator.

In the US, the Airport Noise and Capacity Act of 1990 (ANCA) moved this power to the FAA. An airport that wants a new restriction on Stage 2 or Stage 3 aircraft, such as a curfew, has to go through a Part 161 study, and one that skips the process can lose federal Airport Improvement Program grants and Passenger Facility Charges, according to a 2020 Aviation Pros analysis by Curt Castagna. ¹⁷⁷ As of that article (April 2020), no airport had won FAA approval for a restriction such as a mandatory curfew through Part 161. ¹⁷⁷

Boston Logan has no blanket curfew: Massport's Logan noise rules (740 CMR 24.04) instead bar air carriers' jets that lack Stage 3 certification from 11 p.m. to 7 a.m., and bar jets with no noise certification from landing between 10:30 p.m. and 7 a.m. or taking off between 9:30 p.m. and 7 a.m. ¹⁷⁸

Is supersonic flight over land legal now?

What you hear: a sonic boom is a sharp double bang; NASA's newer design aims for a soft "thump."

Federal rules at 14 CFR 91.817 have banned civil flight faster than Mach 1 over US land without special authorization. On June 6, 2025, Executive Order 14304, "Leading the World in Supersonic Flight," directed the FAA to "repeal the prohibition on overland supersonic flight in 14 CFR 91.817 within 180 days," set an interim noise-based certification standard, and propose and finalize supersonic noise rules under Part 36 within 18 and 24 months. ¹⁷⁹

The FAA's proposed rule, "Enabling Supersonic Overland Flight," would replace the outright ban with a performance standard: supersonic flight over land would be allowed if the sonic boom overpressure at the surface "does not exceed 0.11 pound per square foot (psf)." ¹⁸⁰ The FAA expects early operations to rely on Mach cutoff - flying at a speed and altitude where the boom bends upward before reaching the ground. ¹⁸⁰ The proposal does not regulate focus booms or takeoff and landing noise. ¹⁸⁰

It was published in the Federal Register on July 2, 2026, with comments closing August 17, 2026, and per a DLA Piper summary it had not been finalized; the House passed the Supersonic Aviation Modernization Act (H.R. 3410) in March 2026, which would allow supersonic flight if no boom reaches the ground, and it awaited Senate action. ¹⁸¹ So as of October 2026: proposed, not final.

NASA's X-59 was built to test whether a quieter boom is acceptable. It first flew on October 28, 2025, a 67-minute subsonic flight from Palmdale to Edwards; its target cruise is about Mach 1.4 (925 mph, 1,490 km/h) at 55,000 ft, and NASA aims for "sonic thumps barely audible on the ground," with planned community overflights, ground measurements and resident surveys. ¹⁸² It went supersonic for the first time on June 5, 2026, at about Mach 1.1 and 43,400 ft; the goal is a boom under 75 perceived decibels (PLdB) on the ground, with acoustic validation expected by the end of 2026. ¹⁸³ No overflight schedule for specific towns had been confirmed in the sources checked.

The two numbers use different units and cannot be compared directly: the FAA proposal limits overpressure in psf, while NASA's target is a perceived loudness in PLdB.

Why are helicopters so loud in New York?

What you hear: a low, rhythmic thwop that carries between buildings, often from aircraft flying low along the rivers.

New York City has one of the best-documented helicopter complaint waves in the US. Complaints to 311 about helicopter noise went from 26,218 in 2022 to 59,127 in 2023, according to testimony by NYC Comptroller Brad Lander, who added that "nearly 30,000 tourist trips originate from the Downtown Manhattan Heliport (DMH) at Pier 6." ¹⁸⁴

The legal limit on what a city can do is federal airspace. On April 24, 2025, the City Council passed Intro 26-A, 46-1 with one abstention, barring non-essential, luxury and tourism flights from the East 34th Street and Downtown Manhattan heliports unless they meet strict noise standards, starting in 2029. ¹⁸⁵ The Council said the law would affect about 10% of commercial helicopters using those heliports, and that it can regulate noise but cannot ban flights outright, which is a federal power; whether the mayor would sign it was uncertain at the time. ¹⁸⁵

The mayor did not sign it, and it became law anyway. The Council's legislative record lists Intro 26-A as enacted as Local Law 64 of 2025, with the City Charter rule adopted on May 24, 2025, and the bill marked "Returned Unsigned by Mayor" on May 27, 2025. ¹⁸⁶

New helicopter types have had to meet the FAA's helicopter Stage 3 standard since May 5, 2014. ¹⁶⁵

In Boston, Massport's complaint system notes that information is limited for flights that are not using Logan, such as helicopters and small propeller planes. ¹⁷²

Are delivery drones loud?

What you hear: a high, buzzing whine, quieter than a plane but hard to tune out.

Small drones are far quieter than airliners in absolute terms, but listening studies suggest the sound bothers people more than its level would predict. In a NASA Langley study of 38 listeners, researchers found "a lack of parity between the noise of the recorded sUAS and that of a set of road vehicles," while noting it was unknown whether other factors explained the difference. ¹⁸⁷

A 2025 UK online listening study (Woodcock et al., Frontiers in Acoustics) found annoyance was highest in rural settings, with background levels around 35 dB LAeq, compared with villages (45) and cities (53). ¹⁸⁸ Annoyance rose as the drone got louder relative to the background, up to about 15 dB above it, then leveled off; telling listeners the drone was a medical delivery lowered annoyance. ¹⁸⁸

The study's field measurements put takeoff at about 82 dB LAFmax at 10 m (33 ft) and 66 dB LAFmax at 60 m (200 ft), and an overflight at about 48 dB LAFmax with the drone at 60 m altitude and 44 dB LAFmax at 100 m (330 ft) altitude, measured about 40 m (130 ft) from the flight path. ¹⁸⁸ The authors cite prior work finding drone noise "more annoying than road traffic and conventional aviation noise" at equal exposure. ¹⁸⁸

What plane just flew over, and how do I complain?

Many large airports publish a public flight-tracking map - often a product called WebTrak - that lets you replay what flew over, check altitude and type, and file a complaint by clicking the flight.

The Port Authority of New York and New Jersey's WebTrak, covering JFK, LaGuardia, Newark, Teterboro and Stewart, shows aircraft type, altitude, origin and destination, flight ID and readings from noise monitors in dBA. ¹⁸⁹ Live data is delayed about 21 minutes "for aviation security reasons," you can replay up to 90 days, and complaints go through "Report Aircraft" or the Investigate tab. ¹⁸⁹ Consumer flight trackers show the same flights in close to real time; a guide to those apps is at The Airwaves.

A useful order of operations: note the time, find the flight on the airport's map or a tracker, then file with the airport's noise office, which is the body that logs and answers complaints.

In Boston

Massport takes noise complaints at 617-561-3333 and through an online form, according to the City of Cambridge; Cambridge lists the line as staffed 6 am-5 pm on business days and automated otherwise, with responses typically in 3-4 weeks. ¹⁷² The Town of Wenham lists the same number with 6 am-6 pm hours, so check with Massport. ¹⁹⁰ Massport's "Flight Monitor" shows near-live flight tracks, and the FAA's New England Aviation Noise Ombudsman can be reached at 781-238-7400. ¹⁷²

The Massport Community Advisory Committee represents more than 30 Greater Boston communities and advises the FAA and Massport on noise abatement. ¹⁹⁰ In April 2012 it voted to abandon the Preferential Runway Advisory System, saying it "failed to achieve the intended noise abatement." ¹⁹⁰

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10Construction, backup beepers and leaf blowers

The short version: The standard US table of construction noise comes from the Federal Highway Administration, and its numbers trace back to the specifications Boston wrote for the Big Dig. Measured at 50 feet, an impact pile driver hits about 101 dBA Lmax, a concrete saw 90 and a jackhammer 89. The backup beep exists because US federal workplace rules require a reverse alarm audible above site noise - but OSHA has said that alarm does not have to be a beep, which is why some trucks now hiss instead. Gas leaf blowers measure roughly 65-80 dBA at 50 feet and carry far because of their low-frequency sound; electric models measured about 10 dB quieter in one study, and whether to ban gas blowers is an active local fight.

How loud is a jackhammer?

What you hear: A rapid, metallic hammering that rattles windows, usually starting right when the work day does.

In the FHWA's table, a jackhammer measured 89 dBA at 50 feet (15 meters), against a specification limit of 85.¹⁹¹ All the figures below come from that same table, Table 9.1 of the FHWA Construction Noise Handbook, which feeds the agency's Roadway Construction Noise Model (RCNM) - the software US highway projects use to predict construction noise.¹⁹¹

Every number is Lmax in dBA, slow meter response, at 50 feet. Lmax is the highest level reached during the measurement - the peak moment, not an average over the day.¹⁹¹

Source for every row: FHWA Construction Noise Handbook, Table 9.1.¹⁹¹

Two things stand out. The impact tools - pile drivers, hoe rams, jackhammers, saws - sit at the top, and several machines measured louder than the spec that was supposed to limit them. The pile drivers came in 6 dB over.¹⁹¹ Decibels are logarithmic, so 6 dB is about four times the sound energy.

Why does every US construction noise table look the same?

What you hear: Nothing - but if you have ever read an environmental impact statement for a road or rail project, you have seen these numbers.

The RCNM equipment list was not built from scratch. The FHWA handbook says its specification values come from the Central Artery/Tunnel (CA/T) project - Boston's "Big Dig" - specifically CA/T specification 721.560.¹⁹¹ The spec limits were set at levels the CA/T contractors could achieve, and the handbook notes that pile drivers often exceeded spec.¹⁹¹

So a noise study for a highway widening in Texas or a transit line in California today may be leaning, at least in part, on limits written for one Boston megaproject. That helps explain why so many of the limits come in round fives (80, 85, 90, 95): they began as contract limits, not reference values.

Why are construction numbers always "at 50 feet"?

What you hear: A jackhammer that sounds like it is in the room when you are across the street, and fades to a tapping a block away.

Distance changes everything, so a decibel figure with no distance is close to meaningless. The RCNM table fixes the distance at 50 feet so every machine can be compared on the same footing.¹⁹¹ For a single machine in the open, sound drops by roughly 6 dB each time the distance doubles. By that rule of thumb, an 89 dBA jackhammer at 50 feet would be around 83 dBA at 100 feet and around 77 dBA at 200 feet, before buildings, walls or other sounds get involved. Reflections off a street canyon can make the real drop smaller.

Two cautions when you hold these numbers up against a city noise rule:

• Lmax is not Leq. A city limit written as an average over time (Leq) and a peak reading (Lmax) measure different things. A jackhammer's 89 dBA Lmax does not mean the average level on the block is 89.
• The measuring point matters. Many city codes measure at the property line of the person complaining, not at 50 feet from the machine. Check what distance and metric your local rule uses before comparing.

Why do trucks beep when they back up?

What you hear: Beep... beep... beep, steady and piercing, at 6 a.m., from a dump truck you cannot see.

In the US, the beep comes from OSHA's construction rules. Under 29 CFR 1926.601(b)(4), no employer may use motor vehicle equipment with an obstructed rear view unless "the vehicle has a reverse signal alarm audible above the surrounding noise level" or "the vehicle is backed up only when an observer signals that it is safe to do so."¹⁹² A parallel rule for earthmoving and compacting equipment, 1926.602(a)(9)(ii), requires "a reverse signal alarm distinguishable from the surrounding noise level" or an employee signaling.¹⁹²

Read those carefully and you can see why backup alarms are so loud: the legal test is to be heard over a construction site, which is itself one of the loudest places in a city. An alarm tuned to cut through a running excavator will carry a long way down a quiet residential street. The rule also offers an alternative - a human spotter - which is why you sometimes see a worker waving a truck back with no beeping at all.

Alarms are sold in loudness classes. The SAE J994 standard rates them with a microphone 4 feet (about 1.2 m) from the horn on its axis: Type A at 112 dBA, Type B at 107 dBA, Type C at 97 dBA, Type D at 87 dBA and Type E at 77 dBA. ¹⁹³ Those are the standard's class levels, not field measurements on a street.

Why do some backup alarms sound like static instead of beeping?

What you hear: A harsh "shhh-shhh-shhh" pulse, like bursts of radio static, from a reversing truck.

That is a broadband or "white noise" backup alarm: instead of a single pitch, it hisses across a wide spread of frequencies. In a May 27, 2004 interpretation letter, OSHA wrote that the reverse-alarm provisions "by their terms, do not specify that a reverse signal alarm be of the single-tone type," and that a white-noise alarm complies if it warns workers in, or walking toward, the vehicle's path in time.¹⁰⁶

The appeal is direction. The brain locates a sound by comparing the timing and level differences between your two ears and by the way your outer ear filters sound, and those cues work best on broadband sound with lots of frequencies in it.⁹⁵ A pure beep gives the brain less to work with, especially when it bounces off buildings - which is why a tonal beeper seems to come from everywhere at once. A hiss spread across many frequencies gives a worker more cues to tell where the truck is. The OSHA letter itself rules only on compliance; it does not require or recommend one type over the other.¹⁰⁶

In the UK, broadband alarms are not a legislative requirement, according to the Considerate Constructors Scheme's best-practice hub (January 2020). ¹⁹⁴ It describes a City of London project, 21 Moorfields, that required broadband-only alarms on all delivery vehicles to cut neighbor disruption and to comply with the City of London's construction code of practice. ¹⁹⁴

What time can construction start?

What you hear: Engines turning over and the first jackhammer hits before your alarm goes off.

In the US there is no national construction-hours rule. Hours come from city and town noise codes, usually a weekday daytime window with stricter limits at night and on weekends, and many cities issue after-hours permits for work that cannot happen in daylight, such as road and rail jobs. Who makes the noise rules covers the specific hours, permits and decibel limits in Boston, New York and other cities, and how to report work outside them.

How loud is a leaf blower?

What you hear: A high, droning whine that rises and falls as the operator sweeps, often with a lower engine growl underneath.

Gas leaf blowers can exceed 100 dBA at the operator's ear and typically measure 65-80 dBA at 50 feet.¹⁹⁵ A 2016 study of North Carolina university groundskeepers found their leaf blower noise exposure averaged 89 dBA and peaked at 106 dBA (distance from the machine not given).⁷² For context on the operator's side, the same Wikipedia article cites the NIOSH recommended exposure limit of 85 dBA over an 8-hour workday.⁷² Hearing risk is covered in What noise does to you.

Do not set the 50-foot numbers against the operator-ear numbers as if they were the same thing. The first is what a neighbor across the yard might get; the second is what the person holding the blower gets.

Are electric leaf blowers quieter?

What you hear: A higher, thinner whir with no engine putter underneath.

In the measurements we found, yes. A 2018 study measured three gas models at 67-77 dBA and four electric models at 57-67 dBA, all at 50 feet - roughly 10 dB lower for electric.¹⁹⁵ Indoors, the electric models' levels were 5-19 dBA lower than gas.¹⁹⁵ A 10 dB drop is about a tenth of the sound energy and is usually heard as roughly half as loud.

Why can you hear a leaf blower from blocks away?

What you hear: A blower you cannot see, somewhere a few streets over, still audible through closed windows.

The answer is in the low end. A 2018 Arup study, as summarized in a December 2020 report to the Village of Scarsdale, New York, found gas blowers have "a significantly greater low frequency sound component" than electric ones.¹⁹⁶ In that study all the tested gas blowers were audible at 800 feet (about 245 meters), while none of the electric ones could be distinguished from background sound at that distance.¹⁹⁶

Low-frequency sound loses less energy to the air and passes through walls and windows more easily than high-frequency sound. A-weighted decibels (dBA, explained in Sound and decibels) also deliberately turn down the low frequencies to match how the ear hears quiet sounds, so a dBA reading can understate how far a low engine drone carries. Two blowers with similar dBA figures at 50 feet can sound very different three houses away.

Who bans leaf blowers, and why is it a fight?

What you hear: Depending on your street, either more blowers or suddenly far fewer.

Leaf blower rules started as noise ordinances. Carmel-by-the-Sea, California banned them as a noise nuisance in 1975 and Beverly Hills followed in 1978.⁷² Newer rules increasingly target gas engines for both noise and air pollution:

• Washington, DC: the Leaf Blower Regulation Amendment Act of 2018 barred gas-powered blowers effective January 1, 2022.⁷²
• California: AB 1346, by Assemblymember Marc Berman, passed in October 2021. It halts the sale of most new gas leaf blowers, mowers and other small off-road engines by 2024 (generators by 2028); existing equipment can still be used, and the bill "barely passed."⁷³
• Seasonal bans: Scarsdale, New York bans gas blowers from June 1 to September 30.¹⁹⁶
• Phase-outs: Portland, Oregon is phasing out gas blowers from 2026, with a ban in 2028.⁷²
• The other direction: Georgia and Texas have limited local governments' power to restrict gas equipment.¹⁹⁵

More than 100 US jurisdictions restrict gas blowers, according to Fine Homebuilding; other counts run higher, and the sources do not agree on one number.¹⁹⁵

The arguments, as the two sides put them. Supporters cite noise, emissions and health: Environment New Jersey's Doug O'Malley said one hour of use pollutes as much as driving a car 1,100 miles, and Montclair, New Jersey ban advocate Jessica Stolzberg said the town became "healthier, cleaner, quieter."⁷⁴ Opponents cite cost and practicality: Rich Goldstein, president of the New Jersey Landscape Contractors Association, said his firm has $150,000 to $200,000 in gas blowers ("What am I supposed to do, throw them in the garbage?"), that battery models are less capable, and that charging means retrofitting trucks; contractors challenged Montclair's ban in court.⁷⁴

What about lawn mowers?

What you hear: A steady engine drone, lower and more constant than a blower.

Mowers usually travel in the same legal bundle as blowers. California's AB 1346 covers gas mowers along with blowers and other small off-road engines.⁷³ New South Wales, Australia, groups mowers and leaf blowers together as garden tools with restricted hours (below).⁶⁸

Electric mowers are quieter, though not silent. In a 2005 newsletter from the Noise Pollution Clearinghouse, an advocacy group, a typical gas mower measured 85 to 90 dBA at the operator (90 to 95 for riding mowers), while electric lawn equipment was usually 80 dBA or less. ¹⁹⁷ At 25 feet, electric mowers measured 60 to 65 dBA and quieter gas mowers 70 to 75 dBA. ¹⁹⁷

In Boston

The city's clearest fingerprint on construction noise is national: the FHWA's standard equipment noise limits come from the Big Dig's specification 721.560, written for the Central Artery/Tunnel project that rebuilt downtown's highways.¹⁹¹

Next door, the Cambridge City Council passed an updated leaf blower ordinance in December 2023. Since March 15, 2025, property owners have not been allowed to use gas blowers on their own property; commercial operators, owners of adjoining parcels totaling two or more acres, city employees and city contractors could keep using them until March 15, 2026. Use of any blower is limited to March 15-June 15 and September 15-December 31, on weekdays 8 a.m.-5 p.m. and Saturdays 9 a.m.-5 p.m., and not on Sundays or legal holidays, apart from set hours on Veterans Day and Indigenous Peoples' Day.¹⁹⁸

The city's leaf blower page says that since March 15, 2026, those remaining users are also limited to electric blowers.¹⁹⁹ A License Commission summary revised February 13, 2026, says all gas leaf blowers "have been banned," but still lists narrow exceptions for municipal contractors: residential street cleaning (while the city does not tow for it), parcels of one acre or larger, and emergencies. The two city sources differ on that point. The summary also caps electric blowers at 65 dBA, as rated by the manufacturer under the ANSI standard.²⁰⁰ Permits, fines and the rules in Brookline and other neighboring towns are in The sound of Boston.

For Boston's construction hours and how to report after-hours work, see Who makes the noise rules and The sound of Boston.

Elsewhere in the world

Outside the US, garden equipment is more often handled with set hours than with bans.

• New South Wales, Australia: power tools and garden tools, including mowers and leaf blowers, may not be heard inside a neighbor's habitable room from 8 p.m. to 7 a.m. on weekdays and 8 p.m. to 8 a.m. on weekends and public holidays.⁶⁸
• Toronto, Canada: the noise bylaw (Chapter 591) prohibits power devices such as lawn equipment from 7 p.m. to 8 a.m., extended to 9 a.m. on weekends and holidays.⁶⁷
• European Union: Directive 2000/14/EC caps the sound power (LWA, not a level at a distance) of new lawnmowers by cutting width - 96 dB for widths up to 50 cm under its first stage - and requires leaf blowers only to carry their guaranteed sound power level next to the CE mark. Article 17 leaves member states free to regulate use in areas they consider sensitive.²⁰¹
• Germany: under the federal equipment and machinery noise ordinance (32. BImSchV), mowers may not run in residential areas on Sundays and public holidays or from 8 p.m. to 7 a.m. on workdays, and leaf blowers are also barred on workdays from 7 to 9 a.m., 1 to 3 p.m. and 5 to 8 p.m., according to Berlin's environment department. The same Berlin page says leaf blowers may be used only from September to February, with exceptions for public services.²⁰²

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11The hum: machines, transformers and mystery noises

The short version: Most city hums are electrical or mechanical. Transformers and other magnetic equipment hum at twice the grid frequency - about 120 Hz in North America, about 100 Hz in Europe and most of the world - because their iron cores flex twice in every cycle of the current. Cooling fans, chillers and backup generators add steadier drones, and data centers have drawn organized complaints and new local limits in Virginia and Arizona. A few hums have no agreed source at all; the Windsor Hum in Ontario is the rare case where researchers named a likely culprit, a steel plant across the river in Michigan, and in mid-2020, as the plant was being idled, the lead researcher said he had not heard it for almost a year.

Why does electrical equipment hum?

What you hear: A low, steady, slightly buzzy tone from a transformer box, a substation, a fluorescent fixture or a power adapter, the same pitch day and night.

Power grids deliver alternating current that reverses direction 50 or 60 times a second.²⁰³ In a transformer, motor or other piece of magnetic equipment, that current drives a magnetic field through an iron core. The field reaches a peak twice in every cycle - once in each direction - so the force on the core pulses at twice the grid frequency.²⁰³

On top of that, the core steel itself changes shape very slightly when magnetized, an effect called magnetostriction. As the field rises and falls, the laminated steel sheets stretch and relax, and the whole core vibrates like a small loudspeaker.²⁰³ The result is mains hum: a fundamental tone at twice line frequency, with strong harmonics above it that give it a buzzy edge rather than a pure tone.²⁰³

Because the pitch is locked to the grid, mains hum does not drift. A sound that holds exactly the same note for hours is a strong hint that something electrical is involved.

Why is the hum 120 Hz in North America and 100 Hz in Europe?

What you hear: The same transformer drone, pitched slightly lower in Europe than in North America.

The hum follows the grid. Doubling the line frequency gives:

Source for the frequencies: EPFL Graph Search, "Mains hum."²⁰³ The country examples are a general guide to which grid each place uses.

Japan is split down the middle: eastern Japan runs a 50 Hz grid and western Japan a 60 Hz grid, because Tokyo Electric Light bought a 50 Hz German AEG generator in 1895 and Osaka Electric Light a 60 Hz General Electric generator two years later.²⁰⁴ The two halves trade power through frequency converter stations, the first of which, a 300-megawatt station at Sakuma, was completed in 1965.²⁰⁴

The same source notes that aircraft, which run on 400 Hz power, produce a correspondingly higher hum.²⁰³

What is the 60 Hz buzz in my speakers?

What you hear: A low drone from a stereo, guitar amp or PA that gets louder when you plug in another cable.

This one is different. Hum that leaks into audio equipment, often through a ground loop, sits at the line frequency itself - 60 Hz in North America, 50 Hz in 50 Hz countries - rather than at double it, according to the same EPFL summary.²⁰³ So a hum that pitch-matches about 60 Hz in your own sound system points at the wiring of your gear, while a hum near 120 Hz from outside points at magnetic equipment.

Why do transformers and power lines hum?

What you hear: A drone from a green pad-mounted box on the sidewalk or a fenced substation; sometimes a crackle or sizzle from high-voltage lines, louder in damp weather.

Transformers are the classic source, for the magnetostriction reasons above.²⁰³ High-voltage power lines can also hum through corona - electrical discharge into the air around the conductor.²⁰³ For how electricity gets from power plants to your street, see How a City Works: power.

Substation hum falls off quickly with distance. For a utility substation in Arlington, Washington, with two 28-MVA transformers, a 2016 acoustical analysis predicted up to 50 dBA at the substation's property lines and 23 to 26 dBA at homes more than 1,000 feet away, against limits of 60 dBA and 57 dBA.²⁰⁵

What about rooftop units, chillers and generators?

What you hear: A whooshing fan roar from a building roof or a back alley, cycling on and off; or a diesel engine that starts up, runs at a steady pitch for a while and shuts down.

HVAC equipment - rooftop air-handling units, condensers, chillers, cooling towers - makes a mix of fan noise and motor or compressor hum. Cooling towers can reach up to 70 dBA within 400 feet (about 120 meters), according to the Environmental and Energy Study Institute (EESI), though its figure is for cooling towers at gas-fired power plants rather than data centers.²⁰⁶

Generators are louder. On construction sites, the FHWA measured a generator at 81 dBA Lmax at 50 feet (see Construction and leaf blowers).¹⁹¹ EESI puts industrial diesel generators at up to 105 dB (the article does not give the weighting or distance), so those two figures cannot be compared directly.²⁰⁶ Backup generators at data centers are tested at least monthly, which neighbors may notice as a recurring roar on a schedule.²⁰⁶

Why are data centers so loud?

What you hear: A constant whooshing drone at the edge of a neighborhood, strongest at night when everything else goes quiet, plus a periodic diesel roar.

The noise is mostly cooling. EESI reports that cooling systems use about 40% of a data center's electricity, and the fans, chillers and cooling towers run around the clock.²⁰⁶ Much of the sound energy sits at low frequencies. Kyle Hart of NPCA told EESI that low-frequency content is hard to measure with standard meters.²⁰⁶ A-weighted meters (dBA, explained in Sound and decibels) turn down low frequencies by design, so a reading that looks modest can understate a drone that residents find intrusive.

Proximity makes it worse. A 2024 review by Virginia's Joint Legislative Audit and Review Commission (JLARC), cited by EESI, found nearly one-third of Virginia data centers sit within 200 feet of residentially zoned property.²⁰⁶

Chandler, Arizona is one of the most cited cases. Residents of the Brittany Heights neighborhood complained of a nighttime hum after a data center arrived in late 2014; the city passed a zoning amendment in 2022, and in 2025 the council voted against a new center.²⁰⁶ According to the Prince William Times, a Chandler ordinance from January 2023 requires resident meetings, a paid noise liaison and a pre-construction acoustics baseline, and says post-opening noise may not raise neighborhood levels above what existed before.²⁰⁷

On the industry side, EESI reports that Amazon is retrofitting acoustical shrouds at sites in Northern Virginia.²⁰⁶

Who sets data center noise limits?

What you hear: The same hum, judged very differently depending on which side of a county line you live on.

Limits are local and vary widely. As reported by the Prince William Times in February 2023 (weighting not stated in the article):²⁰⁷

Source: Prince William Times, 2023-02-27.²⁰⁷

Because the article does not say whether these are dBA, they should not be compared with dBA limits elsewhere in this guide. Warrenton's band-by-band approach is aimed at the problem described above: a single A-weighted number can miss low-frequency hum.²⁰⁷

What is "the Hum"?

What you hear: A low drone or throb, often described as like a distant idling engine, that you hear indoors at night - and that the person next to you may not hear at all.

"The Hum" is the name given to persistent low-frequency sounds reported by some residents in particular places, which others in the same place cannot hear. Most reported hums remain unexplained, and proposed causes range from industrial sources to effects inside the listener's own hearing. There is no single agreed explanation, and different researchers argue for different causes.

Three cases come up most often, as summarized by Live Science in 2013.²⁰⁸ In Taos, New Mexico, residents began complaining of a low rumble in spring 1991; researchers from Los Alamos and Sandia national laboratories and the University of New Mexico could not identify the source. In Bristol, England, about 800 people reported a steady thrumming in the 1970s, which was eventually attributed to vehicle traffic and factories running 24-hour shifts. In Kokomo, Indiana, a 2003 study funded by the city found two industrial sites, one a DaimlerChrysler plant, producing noise at specific frequencies, yet some residents kept complaining after noise-abatement measures.²⁰⁸

The Windsor Hum

What you hear: A low rumble that residents of Windsor, Ontario reported for years, traced by researchers to the other side of the border.

Residents of Windsor began reporting a hum around 2011.²⁰⁹ A study by the University of Windsor and Western University pointed across the border to Zug Island in River Rouge, Michigan, home to U.S. Steel blast furnaces.²⁰⁹ The work was funded by Canada's Department of Foreign Affairs and International Trade.²¹⁰

U.S. Steel scaled back operations on Zug Island from April 1, 2020. In July 2020 researcher Colin Novak said, "I haven't heard it for almost a year."²¹¹ The final report came out in July 2021. Novak said the blast furnaces were "really the only type of noise emitter that could do that," and that the hum was not expected to directly harm health but could annoy people or disrupt sleep.²¹⁰

Not everyone agreed. Researcher Glen MacPherson doubted Zug Island was the sole source and suggested some reports reflect a wider "world hum."²¹²

The Windsor case shows how hard tracing a hum can be: it took a multi-year, cross-border study, and the strongest evidence came when the suspected source shut down.

How to track down a hum

What you hear: Something low and steady that you cannot place, and you want to know whether it is a machine, a neighbor or your own ears.

These steps follow from what the sources above describe. None replaces a professional acoustic survey.

1. Note the pattern. A hum that holds exactly one pitch around the clock suggests electrical equipment locked to the grid.²⁰³ One that rises and falls with heat or time of day suggests cooling equipment. One that appears on a schedule for a while, then stops, may be a backup generator test - data center generators are tested at least monthly.²⁰⁶
2. Estimate the pitch. A free tone-generator or tuner app can help you match it. Near 120 Hz in North America (100 Hz in 50 Hz countries) points to transformers and magnetic equipment; near 60 Hz (or 50 Hz) inside your own sound system points to your audio wiring.²⁰³
3. Walk it. Check whether it gets louder near a transformer box, substation, rooftop unit, cooling tower or generator enclosure. Industrial sources can carry a long way: in Windsor, the likely source was on the other side of an international border.²⁰⁹
4. Ask a neighbor to listen. If others hear it, it is more likely an external source. If only some people hear it, that is the pattern reported in many unexplained hum cases.
5. Do not trust a dBA reading alone. A-weighted meters, including most phone apps, discount low frequencies, and low-frequency content is hard to measure with standard meters.²⁰⁶ A low reading does not mean the hum is imaginary.
6. Report it to the right office. Equipment noise from a utility, a building's mechanical system or a facility usually falls under your city's noise code. Who makes the noise rules explains who handles what.

Elsewhere in the world

The physics travels, but the pitch does not: in 50 Hz countries such as the UK, the EU states and Australia, transformer hum centers on 100 Hz rather than North America's 120 Hz.²⁰³ The best-documented traced hum in our sources sits on the US-Canada border, where Canadian residents and researchers pointed to a US plant.²⁰⁹

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12Sounds made on purpose: crosswalk beeps, EV hums and station jingles

The short version: Some city sounds are designed, specified and tested so that someone can act on them without looking. In the US, accessible pedestrian signals tick once a second to help blind pedestrians find the push button and switch to a rapid tick or a spoken message when it is time to walk. Electric cars must play an artificial sound at low speed - up to 30 km/h (18.6 mph) under the US rule, about 20 km/h under the EU and UN rule - and Japan's stations and crossings have turned the same job into short melodies.

Why do crosswalks make a machine gun sound?

What you hear: a slow, quiet tock once a second while you wait, then a burst of fast clicking when the walk sign comes on.

That fast clicking is the rapid tick, the walk indication on an accessible pedestrian signal (APS)²¹³. An APS gives blind and low-vision pedestrians the same information sighted people get from the walk symbol, and in the US its behavior is set by the federal Manual on Uniform Traffic Control Devices (MUTCD). Per an orientation and mobility specialist's summary of the 2009 edition, an APS has three main sounds²¹⁴:

The locator tone lasts 0.15 seconds at most, and the signals are "intended to be loud enough to be heard only at the beginning of the crosswalk"²¹⁵. Volume adjusts automatically to the noise around the pole, so the same signal is louder at rush hour than at 3 a.m.²¹⁴

Older US signals used a cuckoo for north-south crossings and a chirp for east-west. They worked poorly: a pedestrian had to know which compass direction they were facing, and mockingbirds could imitate them, according to KQED²¹³. San Francisco had 283 APS intersections as of KQED's January 2020 reporting²¹³. For the hardware inside the push button, see Street Code's guide to crosswalk signal gear.

In the 2009 edition of the MUTCD, APS rules sat in Chapter 4E, with the locator tone in Section 4E.12²¹⁶; the current 11th edition (2023) puts them in Chapter 4K²¹⁷. California's 2026 manual, which adopts the 2023 federal edition with state amendments, lays out that chapter - including 4K.03, Walk Indications, and 4K.04, Vibrotactile Arrows and Locator Tones.

Under that text, walk tones and locator tones should be no more than 5 dBA louder than ambient sound; automatic volume adjustment is required up to a maximum of 100 dBA; tone walk indications repeat at eight to ten ticks per second; and locator tones should be audible 6 to 12 feet from the push button²¹⁸. The often-quoted 89 dBA maximum does not appear in that text.

What does the beeping at a crosswalk mean?

What you hear: a steady beep or tock from the push-button box, even when nobody is crossing.

Usually it is the locator tone, which repeats once per second throughout the "don't walk" phase²¹⁴. It is not a warning and does not mean the light is about to change. It is a beacon, kept quiet enough to be heard near the pole²¹⁵. When the walk phase starts, the sound changes character - to the rapid tick or the speech message - and that change is the signal to go²¹⁴.

Why do crossings in Japan play bird songs and music?

What you hear: a two-note "beep-boop" or a "piyo" chirp at a Tokyo crossing, or a few bars of a children's song.

Japan's accessible signals mostly use bird chirps or melodies, and municipalities choose the sounds. In the count reported by walkinginfo.org, about 10,570 of roughly 170,000 signalized intersections had APS - a dated figure - and the signals were usually switched off at 8 p.m. because of noise complaints²¹⁹. In Tokyo, Metropolis describes a "beep-boop" for east-west crossings and a "piyo" for north-south, and the nursery song "Toryanse" is sometimes heard at crossings¹¹¹.

The trade-off is visible here. Melodies are pleasant and distinctive, but direction-coded sounds rely on the listener knowing which way is which - the same problem that retired the US cuckoo and chirp²¹³.

What is the "tick-tock" and "kapow" at Australian crossings?

What you hear: a slow chirp while you wait, an urgent "tick-tock-tick-tock" to cross, and a single "kapow" when the signal changes.

That is the PB/5 pedestrian push button, designed in Australia in 1984 by a team of David Wood, Louis Challis and Frank Hulscher²²⁰. The slow chirp is its locator; the rapid "tick-tock" means cross; the "kapow" marks the change of state. A built-in microphone tracks traffic noise and adjusts the volume²²⁰. It is used in Australia, Ireland, New Zealand, Singapore and the US²²⁰.

Why do electric cars make a sound at low speed?

What you hear: a soft, rising whir or synthetic hum from an electric car pulling out of a parking space, which fades as it speeds up.

At low speed an electric or hybrid car makes far less noise than a combustion car, so governments require an artificial warning sound. In the US the rule is Federal Motor Vehicle Safety Standard (FMVSS) 141, which grew out of the Pedestrian Safety Enhancement Act of 2010²²¹. In rulemaking, NHTSA cited a study in which hybrids had a pedestrian crash rate 1.18 times that of conventional vehicles²²¹.

FMVSS 141 requires sound when the vehicle is stationary but not in Park, in reverse, and moving forward up to 30 km/h (18.6 mph)²²¹. The rule phased in with 50% of production by September 1, 2019 and full compliance by September 1, 2020²²¹. Under one of the compliance options, sounds that meet the standard at 30 km/h measure roughly 60 to 64 dBA overall²²¹.

In Europe the device is called an Acoustic Vehicle Alerting System (AVAS). EU Regulation 540/2014, Article 8, required AVAS on new types of hybrid and pure electric vehicles from July 1, 2019 and on all new ones from July 1, 2021²²². AVAS sounds up to about 20 km/h and in reverse²²³.

The UN test, UN Regulation 138, places microphones 2 m from the vehicle center line. Forward sound at 10 and 20 km/h must not exceed 75 dBA, and the pitch must rise by at least 0.8% per km/h on average, so the sound itself tells you the car is speeding up²²⁴. China's GB/T 37153 mirrors R138 with minimum levels 2 dB higher²²⁴.

The minimum levels in R138, as published in the EU's Official Journal in January 2017, are 50 dBA at a constant 10 km/h, 56 dBA at 20 km/h and 47 dBA in reverse²²⁵. Japan's transport ministry issued guidelines for these devices in January 2010²²⁶. The ministry's guideline text calls for a device that sounds automatically from starting up to 20 km/h and in reverse, with a continuous sound that suggests a running vehicle; sirens, chimes, melodies and animal calls are listed as unsuitable, and a driver-operated pause switch is allowed²²⁷.

At what speed does an electric car's warning sound turn off?

Above the crossover speed - the point where tire-on-road noise (see Traffic) becomes loud enough to do the job - the artificial sound is no longer required. The two main rules draw that line in different places: 30 km/h (18.6 mph) in the US and about 20 km/h in the EU²²¹²²³. NHTSA considered lowering the US crossover to 20 km/h and declined; the National Federation of the Blind backed keeping it at 30 km/h²²¹. The US rule also requires sound when the car is stopped in gear, which the EU summary does not mention²²¹²²³.

The same idea is reaching heavy vehicles. When New York City's Sanitation Department piloted a Mack LR Electric refuse truck from November 2020, the truck was described as "near-zero" noise, with white noise added so people nearby would know it was there¹⁴².

What is the little tune before a train leaves in Japan?

What you hear: a cheerful jingle of about seven seconds on the platform, right before the doors close.

That is a hassha melody (departure melody). Japanese railways adopted melodies partly as noise reduction and passenger service, because the metal bells used by Japanese National Railways were unpopular²²⁸. Early examples include Bungo-Taketa Station, which played "Kojo no Tsuki" from a 1951 record, and the Keihan railway, which began a melody in August 1971. After privatization, Sendai became the first JR East station with melodies on November 22, 1988, and Shinjuku and Shibuya followed on March 11, 1989. About seven seconds is considered the ideal length²²⁸.

Some stations have signature tunes: Ebisu plays "The Third Man Theme" and Takadanobaba plays the Astro Boy theme²²⁸. Metropolis credits the 1989 jingles to Hiroaki Ide and says Minoru Mukaiya has composed around 170 since 2003¹¹¹. In February 2025, JR East announced it would phase out local platform melodies in favor of standard melodies played from the trains themselves²²⁸.

Other station sounds in Tokyo serve as guidance: bird-like sounds lead visually impaired riders to exits, and escalators announce their location¹¹¹.

In Boston

In Massachusetts, MassDOT committed, effective June 1, 2012, to install APS at all new traffic signals and, when possible, at existing signals during a major alteration or reconstruction; retrofits at MassDOT-maintained locations are considered on request²²⁹.

On the MBTA (more T sounds are in Trains and subways), the new Orange and Red Line cars came with a "door open chime" meant to help blind and low-vision riders find the doors, an idea the T's accessibility office compared to audible crossing signals. After complaints about loud, constant beeping, the T had 11 riders test five replacement sounds in late 2022; by March 2023 a less frequent chime was on 64 of 82 new Orange Line cars and all 12 new Red Line cars, the Boston Globe reported²³⁰.

Elsewhere in the world

• Japan: municipally chosen bird chirps and melodies at crossings, usually off after 8 p.m.; station departure melodies since 1988-89 on JR East²¹⁹²²⁸.
• Australia, New Zealand, Ireland, Singapore: the PB/5 locator chirp, "tick-tock" and "kapow"²²⁰.
• European Union: AVAS mandatory on all new electric and hybrid cars since July 1, 2021²²².
• China: GB/T 37153 follows UN R138 with minimums 2 dB higher²²⁴.
• Station jingles beyond Japan: Denmark's DSB, France's SNCF (a jingle by Michael Boumendil), Switzerland's vibraphone jingles and, since 2023, Singapore SMRT chimes based on local tunes²²⁸.

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13Music, nightlife and crowds

The short version: Amplified shows commonly run above 100 dB, and research at real concerts has found front-row bass peaks above 140 dBC where subwoofers sit on the ground. The World Health Organization's 2022 voluntary standard asks venues to keep the audience average at 100 dB LAeq over 15 minutes, while France and Switzerland write similar caps into law and the US has no federal audience limit. Fights between venues and new neighbors are increasingly handled through "agent of change" planning rules, night mayors and mediation rather than police calls. Crowds and civic sounds such as bells and calls to prayer sit in the same rulebooks, usually as exemptions or time windows.

How loud does a concert or club actually get?

What you hear: Music you feel in your chest, ears that ring on the walk home, a muffled world the next morning.

The American Academy of Otolaryngology-Head and Neck Surgery (AAO-HNS), citing a 2021 study in Laryngoscope, says sound at US music venues "commonly exceeds 100 dB."²³¹ More detailed numbers come from Audio Engineering Society (AES) research on monitoring data from more than 300 tour dates, festivals and one-off shows, summarized by ProSoundWeb:²³²

• At the front row, where data existed, peaks topped 140 dBC, and 5-minute averages ran 120-130 dBC when subwoofers were stacked on the ground.
• A handful of engineers mixed above 103 dBA averaged over at least 5 minutes, usually only for a few minutes during encores.
• At festivals, touring engineers mixed about 3 dBA louder than house engineers, and levels rose about 4 dBA from small crowds to large ones. On tours, indoor shows averaged about 1 dBA louder than outdoor ones.
• Shows working under an LAeq limit came out about 2 dBA quieter, and shows under an LCeq limit about 4 dBC quieter.

Those figures use three different measures (all explained in Sound and decibels), and they should not be lined up against each other. A peak (dBC peak) is the single highest instant. An average (Leq) is the steady level that would carry the same energy over a set window, 5 minutes or 15 minutes or an hour. A-weighting (dBA) discounts deep bass roughly the way the ear does at moderate levels; C-weighting (dBC) counts bass more fully, which is why bass-heavy front rows read so much higher in dBC. A 140 dBC peak and a 103 dBA average can describe the same night from two angles.

On the health side (more in What noise does to you), WHO estimates that 40% of people aged 12-35 in high- and middle-income countries are exposed to damaging sound levels at entertainment venues, and that more than 1 billion young people are at risk of hearing loss from avoidable recreational sound.²³³²³⁴

For how the speaker systems behind these numbers are built and tuned, see the sister guide The Show File: concert sound.

Nightclubs have been surveyed less than concerts. Acoustical consultants Andrew Dobson and William Gastmeier measured more than 60 nightclubs in Toronto, Canada, mostly in the city's Entertainment District, and reported in Canadian Acoustics in 2010 an overall average of 96 dBA LAeq, with the highest levels near the dance floors and the bars beside them. Their measurements did not cover full work shifts.²³⁵

What is the WHO safe listening standard for venues?

What you hear: Ideally, less than you would have heard otherwise - and a quieter room off to the side.

WHO released its Global standard for safe listening venues and events under the Make Listening Safe initiative, ahead of World Hearing Day on March 3, 2022. Live sound engineers, manufacturers and academics helped draft it.²³² It is voluntary and has six features:²³³

1. Limit the average sound level to 100 dB LAeq over 15 minutes.
2. Monitor sound levels.
3. Optimize venue acoustics and sound systems.
4. Make hearing protection available.
5. Give access to quiet zones.
6. Train and inform staff.

The first major event to apply the whole standard was the Serendipity Arts Festival in Goa, India, in December 2023: 9 days, more than 1,800 artists, 12 venues. WHO reported that breaches of the limit were "infrequent, minor and short-lived" and that most attendees did not notice a change.²³³

In February 2026 the AAO-HNS published a position statement applying the WHO-based limits to the US and adding several of its own:²³¹

A position statement is guidance from a medical society, not a law. There is no federal limit on audience sound levels in the US.

Which countries cap concert volume by law?

What you hear: A mixing desk with a decibel display facing the engineer, and earplug dispensers by the bar.

France. Decree 2017-1244 of August 7, 2017 caps amplified sound at 102 dB(A) and 118 dB(C), each as a 15-minute equivalent level, anywhere the public has access. Events for children up to age 6 are capped at 94 dB(A) and 104 dB(C). Venues must also inform the public, hand out free hearing protection and provide rest zones or rest periods. Continuous recording of dB(A) and dB(C), with levels displayed at the desk, applies to venues for more than 300 people. Festivals are covered, and existing venues had until October 1, 2018 to comply.²³⁶

Switzerland. The V-NISSG ordinance, in force since June 2019, replaced the 1996 Sound and Laser Ordinance.²³⁷ It works in tiers, measured as an hourly average (LAeq1h) at ear height in the most exposed spot the audience can reach:²³⁷²³⁸

Belgium and Austria. A trade-press summary gives Belgium 100 dBA averaged over 1 hour and Austria 100 dBA over 1 minute, and notes that "most primary limits are around 100 dBA" in Europe, with averaging times that vary.²³² The averaging window matters: a 1-minute limit catches a loud chorus that a 1-hour average would smooth away.

Switzerland also caps the instant level. Under Article 19 of the V-NISSG, the Federal Office of Public Health's enforcement guide (October 28, 2025) says the instantaneous level may not exceed 125 dB(A) LAF,max - A-weighted, fast time weighting of 125 ms - at any time. As with the hourly limits, it applies at the loudest spot the audience can reach, at about ear height.²³⁹

When do outdoor concerts have to stop?

What you hear: A festival headliner drifting across a few miles of city, then silence at 11.

Audience limits protect the people inside the gates. Neighbor limits are a separate set of rules. In the UK, outdoor concerts are judged against the Noise Council's 1995 Code of Practice on Environmental Noise Control at Concerts, known as the "Pop Code."²⁴⁰ It sets a Music Noise Level (MNL), a 15-minute LAeq measured 1 m from the facade of the nearest noise-sensitive homes:²⁴¹

Those limits apply from 09:00 to 23:00. After 23:00, music should not be audible inside noise-sensitive homes with windows open for ventilation. For bass, the Code treats about 70 dB in the 63 Hz or 125 Hz octave bands as satisfactory and 80 dB or more as significant disturbance.²⁴¹

In the US, curfews are mostly set venue by venue, through city permits and local noise codes.

What is the agent of change principle?

What you hear: Nothing new - which is the point. The club was there first, and the new building next door was soundproofed before anyone moved in.

Agent of change means whoever arrives second pays to manage the noise conflict. A developer building homes beside an existing venue pays for soundproofing; a new venue opening beside existing homes must contain its own sound.

• Victoria, Australia (2014). The Live Music Action Agenda, announced August 4, 2014, put the onus on "the party seeking to change the status quo." It promised a planning practice note, a review of the state's music-noise policy (SEPP N-2) and A$500,000 for venue soundproofing.²⁴² New homes near existing venues would need noise mitigation, new venues would have to limit their noise, and the liquor regulator would weigh the principle in complaints.²⁴³
• San Francisco (2015). Ordinance 70-15, sponsored by Supervisor London Breed, passed the Board of Supervisors 11-0 on May 12, 2015.²⁴⁴ A permitted, compliant Place of Entertainment cannot be declared a nuisance over noise complaints from residents of buildings within 300 ft (about 90 m) that were built or converted on or after January 1, 2005. Sellers and landlords within 300 ft must disclose possible noise in writing. New homes must keep interior noise from outside sources to 45 dB, with an acoustic study where outdoor noise exceeds 60 dB Ldn/CNEL.²⁴⁴ A press release for Breed's legislation said it would protect the city's 351 places of entertainment from "unfair complaints."²⁴⁵
• England (2018). After a UK Music-led campaign backed by more than 100 MPs and peers, a draft of the National Planning Policy Framework came out in March 2018.²⁴⁶ The revised NPPF put the principle at paragraph 182: "Existing businesses and facilities should not have unreasonable restrictions placed on them," with the applicant responsible for mitigation.²⁴⁷ It is planning policy, not statute.
• Brussels (2026). In April 2026 a regional parliament committee backed a rule requiring anyone building or renovating within 20 m (about 65 ft) of a nightclub to soundproof, new clubs not to disturb existing residents, and developers and landlords to disclose nearby clubs. It still needs a full parliament vote.²⁴⁸

Supporters, mainly venue and music-industry groups, argue that complaints from new neighbors close venues; one 2025 policy essay links the loss of one in three UK grassroots venues in a decade to such complaints, and notes that "very few cities have actually adopted" the principle.²⁴⁹ The cost shift is written into the laws themselves: San Francisco's version limits nuisance claims by newer residents and puts disclosure and soundproofing duties on sellers, landlords and builders.²⁴⁴

What does a night mayor do?

What you hear: Fewer calls to the police, ideally. A night mayor's job is to be the person venues, neighbors and city hall can all call instead.

Amsterdam pioneered the post with former promoter Mirik Milan. The sources disagree on the year: the Christian Science Monitor says 2012 and calls him "the first night mayor in the world," while Resident Advisor dates it to 2014.²⁵⁰²⁵¹ The Monitor counts more than 50 cities with a similar role.²⁵⁰ London's mayor appointed Amy Lamé as the city's first Night Czar in 2016.²⁵¹

In 2017 a New York City Council member proposed an Office of Nightlife with a "night mayor" and a 12-member advisory board, citing a city report that about 20% of the city's music venues had closed in 15 years.²⁵² Barcelona said it would appoint one after finding nightlife hot spots exceeded WHO-recommended sound levels, and Manchester's night mayor handles noise complaints among other issues.²⁵⁰

New York's office, led by Ariel Palitz from 2018 to early 2023, runs MEND (Mediating Establishment and Neighborhood Disputes), which uses mediation instead of enforcement for venue-neighbor disputes and reports an 80% resolution rate. In its pilot, a club and seven neighbors agreed to talk through a group text.²⁵⁰

How loud is the loudest stadium crowd?

What you hear: A wall of voices that peaks on a third-down play.

Guinness World Records lists 142.2 dBA as the loudest crowd roar at a sports stadium, set by Kansas City Chiefs fans at Arrowhead Stadium in Kansas City, Missouri, on September 29, 2014.²⁵³ It came in the first quarter of a Monday night game against the New England Patriots, with a Guinness adjudicator on site.²⁵⁴ The previous record, 137.6 dBA, was set by Seattle Seahawks fans on December 2, 2013.²⁵⁵

The meter distance and time weighting behind the record were not published. Read it as a peak-style reading, not an exposure average, and do not compare it directly with the 100 dB LAeq venue limits above.

Are church bells and calls to prayer exempt from noise rules?

What you hear: Bells on the hour, or a call to prayer from a minaret loudspeaker.

Religious sound is usually handled in local noise codes through hours or exemptions. In April 2023, during Ramadan, the Minneapolis City Council voted unanimously to remove time limits that had restricted amplified broadcasts to 7 a.m.-10 p.m., which usually ruled out the dawn call. That made it the first major US city to allow all five daily Islamic calls to prayer to be amplified. Observers at the hearing compared it with church bells, and no organized opposition was reported.²⁵⁶ Earlier, Hamtramck, Michigan legalized the amplified call through a noise-ordinance change put to a citywide vote in 2004, which "stirred notable tensions."²⁵⁷

In Boston

Boston's noise ordinance, as reported in 2019, treats sound above 50 decibels from 11 p.m. to 7 a.m. as unlawful and above 70 decibels as excessive at any hour, with permitted construction excepted. The report did not give the weighting. That year, city councilors named arena events and late-night bar crowds among the city's noise sources, and the council president said patrol officers did not carry decibel meters.²⁵⁸

Venue noise cases go to the Entertainment Licensing Board, working with the Mayor's Office of Consumer Affairs and Licensing. The full list of who to call is in The sound of Boston.

Mayor Michelle Wu named Corean Reynolds the city's first Director of Nightlife Economy on February 22, 2023, with a remit covering late-night activity, downtown revitalization and late-night transit. The announcement did not mention noise.²⁵⁹ We found no agent-of-change ordinance in Boston and no agent-of-change bill in Massachusetts, and no Boston mediation program comparable to New York's MEND.

Elsewhere in the world

Europe has the clearest legal audience caps (France, Switzerland, and by trade-press account Belgium and Austria), and the UK's Pop Code governs what neighbors hear from outdoor shows. The agent of change principle started in Victoria, Australia and has spread through San Francisco, England and, pending a final vote, Brussels. Night mayors operated in more than 50 cities by the Christian Science Monitor's 2023 count.²⁵⁰

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14Birds, bugs and the city's wild soundscape

The short version: City birds change their songs to be heard over traffic: studies have found great tits singing higher in noisy parts of Leiden, nightingales singing louder in Berlin traffic, and robins singing at night where daytime noise is high. Insects can rival machines, and the 2024 periodical cicada emergence was reported at 90-100 dB, though the reports gave no distances. Cities and nonprofits now map and protect quiet places, from EU "quiet areas" to certified quiet parks. The 2020 lockdowns showed how much of the background is human: seismometers worldwide recorded up to 50% less high-frequency ground noise, and 11 public sites in London averaged 5.4 dB LAeq quieter than a year earlier.

Why do birds start singing so early in the city?

What you hear: A wall of birdsong before sunrise, sometimes well before.

The dawn chorus is the burst of birdsong around first light. Urban birds can start it earlier than rural birds: in a Leiden University study, urban great tits began singing an average of 22 minutes earlier than rural ones. The same work cites research linking airport noise to earlier dawn choruses (Gil et al., 2015), which suggests birds may be getting their songs in before the morning noise begins.²⁶⁰

Light plays a part too. The Max Planck Society reports that near streetlights, early singers such as blackbirds and robins start earlier, drawing on a study in a forest near Vienna, and that blue tit males started about 15-20 minutes earlier.²⁶¹

Do birds sing higher in cities?

What you hear: A familiar song that sounds slightly thinner or more piping on a busy street than in the woods.

In 2003, H. Slabbekoorn and M. Peet reported in Nature that great tits in noisier territories in Leiden, the Netherlands, sang with a higher minimum frequency. They read this as a learned, flexible adjustment.²⁶² Traffic noise is concentrated in the low frequencies, so moving the bottom of a song upward keeps it from being masked.

The trick works better for some species than others. The Max Planck Society notes that raising pitch helps great tits more than blackbirds, which sing lower.²⁶¹

Do birds sing louder in noisy places?

What you hear: A nightingale that seems to be shouting over the morning commute.

Henrik Brumm recorded 15 male nightingales in Berlin on weekday mornings (about 5-10 a.m.) in spring 2001 and 2002, published in the Journal of Animal Ecology in 2004. Males in noisier territories sang louder, with about 14 dB between the quietest and loudest. Three birds recorded on weekends sang more softly when traffic dropped.²⁶³ Berlin has about 1,500 nightingale breeding pairs, and in aviary tests nightingales sang more forcefully under white noise.²⁶¹

Since decibels are logarithmic, a 14 dB difference is a large one: roughly 25 times the sound energy.

Why is a bird singing at 3 a.m.?

What you hear: A full, melodic song in the dark, often from a tree near a streetlight.

In 2007, R. A. Fuller, P. H. Warren and K. J. Gaston published "Daytime noise predicts nocturnal singing in urban robins" in Biology Letters. They found that daytime noise explained more of the variation in night singing among urban robins than night light did.²⁶⁰ Press coverage of the University of Sheffield work at the time reported noise levels 10 times higher in places where birds were singing at night.²⁶⁴

So the streetlight is not the whole story. The likelier explanation from this study is that robins in loud places move their singing to the hours when the city is quiet enough to be heard.

How loud are cicadas?

What you hear: A pulsing, electric drone from the trees that can drown out conversation.

In 2024, periodical cicada Broods XIII (on a 17-year cycle) and XIX (13-year) emerged together for the first time in 221 years, overlapping in parts of Illinois and Indiana.²⁶⁵ Researchers expected the overlap zone to be small and around Springfield, Illinois, and Gene Kritsky estimated up to about 1.5 million cicadas per acre in the Northern Illinois Brood (XIII).²⁶⁶

NBC Chicago reported that the CDC cites meter and phone-app readings of 90-100 dB for cicadas, "well above" the 85 dB recommended exposure limit.²⁶⁶ The American Academy of Audiology cited reports of 105 dB in clusters of about 1,000 insects, but added that choruses "may not be loud enough to cause a temporary threshold shift."²⁶⁵ None of these reports gave a measurement distance or weighting, so treat them as rough field readings, not exposure levels you can compare with a workplace limit.

Distance changes the picture. In a 2021 explainer, the National Institute for Occupational Safety and Health (NIOSH) said cicada noise measured 3 feet from a heavily infested tree "may approach 100 dBA," and estimated about 94 dBA at 6 feet, 88 dBA at 12 feet and 82 dBA at 24 feet - a drop of 6 dB with each doubling of distance. Those distance figures are estimates, not field measurements.²⁶⁷

Where can you find quiet in a city?

What you hear: Wind, leaves, your own footsteps - and the absence of traffic.

Noise policy has started protecting quiet as well as limiting noise. How quiet is defined and measured is covered in Measuring and finding quiet.

• EU quiet areas. The EU's Environmental Noise Directive lets cities designate and protect quiet areas.²⁶⁸
• Hush City. A citizen-science app developed by Antonella Radicchi at TU Berlin, it lets residents map places they find peaceful. Berlin and Limerick, Ireland have used it for quiet-area planning.²⁶⁹ Limerick asked the public to use it from early 2020, during its year as European Green Leaf city.²⁶⁸
• Quiet Parks International. Co-founded by Gordon Hempton and Vikram Chauhan, it certifies quiet places. Its first Wilderness Quiet Park is the Zabalo River in Ecuador, and its first Urban Quiet Park is Yangmingshan National Park in Taipei, awarded in June 2020.²⁶⁹

The reason for the effort: as reported by Euronews from European Environment Agency figures, 1 in 5 Europeans is exposed to harmful noise, linked to about 12,000 premature deaths a year and 6.5 million people with chronic sleep disturbance.²⁶⁹ What the health agencies say about noise is in What noise does to you.

In the US, the National Park Service's Natural Sounds and Night Skies Division collects baseline data on ambient sound in parks, identifies noise sources and ways to reduce them, and runs an overflights program covering air tours, airspace design and military flights.²⁷⁰

Did cities really get quieter during the 2020 lockdowns?

What you hear (in spring 2020): Birdsong you had never noticed, and a street you could hear across.

Yes, measurably. Scientists sometimes call the period the anthropause. In a July 2020 Science paper, Lecocq, Hicks, Van Noten and colleagues reported a global drop in high-frequency seismic noise - ground vibration from traffic, industry and people moving around - of up to 50%, lasting months. They called it the longest and most prominent reduction on record. It was strongest in populated areas and closely tracked human mobility data.²⁷¹

At ear level, Aletta and colleagues at University College London compared 11 public sites in London in spring 2019 and spring 2020. Average sound levels fell by 5.4 dB LAeq, ranging from 1.2 dB to 10.7 dB depending on the site.²⁷² The size of the drop depended on what normally dominated each spot: places loud with traffic behaved differently from places loud with people.

Note the two measures. The seismic figure is a percentage drop in ground vibration; the London figure is a change in A-weighted airborne sound. Both point the same way, but they are not the same quantity.

In the US, a study of white-crowned sparrows in the San Francisco Bay Area, led by Elizabeth Derryberry of the University of Tennessee, Knoxville, was published in Science in September 2020 as "Singing in a Silent Spring." According to the university, shutdown traffic on the Golden Gate Bridge compared with levels from 1954, and urban San Francisco was no louder than the surrounding rural county. The sparrows sang more softly, but their songs carried about twice as far.²⁷³

In Boston

We found no Boston-specific measurements of the dawn chorus, urban bird song changes, cicada levels, lockdown sound levels or quiet-area mapping. The studies above come from the Netherlands, Germany, Austria, the UK, Illinois and San Francisco. The mechanisms they describe - songs pushed higher, louder or later by traffic noise, and quiet that returns when traffic stops - are general, but how strong they are in any given city has to be measured there.

Elsewhere in the world

Most of the urban birdsong research cited here is European: Leiden for great tits, Berlin for nightingales, the UK for robins, and the Vienna area for the streetlight effect.^262263260261 The EU is also the only jurisdiction here with a legal basis for protecting urban quiet areas, while the first certified Urban Quiet Park is in Taipei.²⁶⁸²⁶⁹

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15Measuring, mapping and finding quiet

The short version: A good iPhone app can get within a couple of decibels of a professional meter, which is enough to learn what is loud around you but not, by itself, enough for a formal case. Noise maps from the EU and the US Bureau of Transportation Statistics are computer models of long-term averages, useful for comparing streets and neighborhoods, not readings at your door. Complaints tend to work best when they follow the ladder that official guidance in several countries recommends: talk first, keep a dated log, use the right channel, and try mediation for neighbor disputes. Finding quiet mostly comes down to distance, something solid in the way, and heavy walls - with bass the hardest to stop.

Can I measure noise with my phone?

What you hear: a sound you suspect is "too loud," and a phone in your pocket.

In 2014 the US National Institute for Occupational Safety and Health (NIOSH) looked at 130 iPhone sound meter apps and tested 10, and looked at 62 Android apps, of which 4 "partially met" its criteria. Three apps came within +/-2 dB of a reference meter on A-weighted readings.¹⁶ The best A-weighted results were SoundMeter (a mean difference of -0.51 dBA), NoiSee (-1.12) and Noise Hunter (-1.92). The researchers found the same Android app showed "wide variance" across devices, and concluded Android and Windows developers did not offer apps that met the needs of occupational noise assessment.¹⁴ In a 2015 follow-up, the same researchers reported preliminary results that, with a calibrated external microphone, apps agreed within +/-1 dB of professional instruments.¹⁷

NIOSH then built its own free NIOSH Sound Level Meter app, announced in January 2017. It runs on iOS only and reports LAeq, Lmax, Lpeak, time-weighted average, dose and projected 8-hour dose, with A, C or Z weighting and slow or fast response. In a lab test it read about 2 dBA off with the iPhone's built-in microphone and within 1 dBA with a calibrated external microphone.¹⁰

For context, a 3 dB change is barely perceptible and 5 dB is readily perceptible,⁹ so a 2 dB app error is smaller than most differences you would notice by ear.

What is a real sound level meter?

Professional meters are graded under IEC 61672-1 as Class 1 (precision) or Class 2 (general purpose). At 1 kHz, the allowed tolerance is +/-1.1 dB for Class 1 and +/-1.4 dB for Class 2; at 20 Hz it widens to +/-2.5 dB and +/-3.5 dB.¹⁵ US practice often uses the older ANSI terms Type 1 and Type 2; OSHA treats a Type 2 meter as accurate to +/-2 dBA.¹⁴ Requirements depend on the job: UK workplace rules require at least Class 2, while unattended aircraft monitoring under ISO 20906 requires Class 1.¹⁵

Some UK councils accept recordings from a phone app, though not as decibel readings. Woking Borough Council says it stores recordings sent through The Noise App and "may use them to investigate noise complaints."²⁷⁴ Wrexham accepts Noise App recordings once a complaint has been formally registered, up to ten per complaint; its guidance does not mention decibel readings.²⁷⁵

How do I take a reading that means something?

Match your settings to the rule you care about (local limits are in Who makes the noise rules; the terms are explained in Sound and decibels), and write down how you measured.

• Weighting. Use dBA for most city limits. Use dBC if the problem is bass and your code has a dBC limit, as New York City and Toronto do.^{64 67}
• Metric. Leq is the steady level with the same energy as the fluctuating sound over the period;⁴ Toronto's amplified-sound limits are 10-minute Leqs.⁶⁷ Lmax is the loudest moment and ignores how long it lasted.⁴
• Background. Several codes judge a noise against the ambient level, such as New York City's 7 dB(A) over ambient at night.⁶⁴ L90, the level exceeded 90% of the time, is a common measure of background.⁷ Take a reading with the source off, if you can.
• Response. Fast time weighting averages over 125 milliseconds, slow over 1 second.⁷ Note which one you used.
• Place and distance. Codes measure at specific points, such as a lot line in Boston⁶² or inside a home 3 feet from an open window for New York City air conditioners.⁶⁴ From a single source, the level drops about 6 dB each time the distance doubles,⁵ so a reading without a distance is hard to use.

How do I read a noise map?

What you see: a city map washed in color bands, red along highways and runways fading to green.

A noise map is a model, not a recording. It calculates long-term average levels from traffic counts, flight paths and terrain.

The EU's first round covered cities over 250,000 people, roads over 6 million vehicles a year, railways over 60,000 trains a year and airports over 50,000 movements; the second round, due June 30, 2012, lowered the thresholds to cities over 100,000, roads over 3 million vehicles and railways over 30,000 trains.¹² Lden is a 24-hour average that adds 5 dB to evening noise (7 p.m. to 11 p.m. by default) and 10 dB to night noise (11 p.m. to 7 a.m.); countries may shift the hours.¹¹ Lnight is the night average alone. The Directive "does not set any limit value."²⁵

The BTS map models worst-case conditions with no shielding from buildings or terrain. It found more than 97% of the US population potentially exposed to transportation noise below 50 dBA (24-hour LAeq).²³ Airport maps in the US use contours, lines joining points of equal level, like the lines on a topographic map.⁴

Three cautions. An Lden value and a 24-hour LAeq value are not the same number, because Lden carries evening and night penalties. A model shows an annual average, not the garbage truck at 5 a.m. And worst-case modeling with no shielding can show a building in a quiet courtyard as loud as one facing the road.

How do I complain about noise effectively?

Official guidance from several countries follows a similar ladder.

1. Talk to the source first. An Australian council's advice is to approach the neighbor tactfully before contacting the council.⁶⁸
2. Keep a log. For barking dogs, that council says you may be asked to keep a diary.⁶⁸ Note dates, times, how long the noise lasted, what it was and how it affected you, plus any readings and how you took them.
3. Check whether it is permitted. In Boston, the city advises checking the after-hours construction permit database before reporting night work.¹¹⁵
4. Use the right channel. In New York City, all noise complaints go to 311.⁶³ Many places split the job: in New South Wales, late-night parties go to police, pubs and clubs to Liquor and Gaming NSW, and aircraft to Airservices Australia.⁶⁸ For aircraft, identifying the flight first makes a complaint easier to act on; The Airwaves covers flight trackers.
5. Separate the noise from the relationship. A New York dispute resolution group suggests filing with 311 for the noise and contacting a mediation service, such as the New York Peace Institute, for the relationship with the neighbor.²⁷⁶

Volume is not the same as action. New York City's 311 took more than 738,000 noise complaints in 2024.¹

The most complete public figures are old. A January 2018 New York State Comptroller report on 2010 through 2015 found that DEP investigated about 230,000 noise complaints and issued fewer than 6,000 violations, while the NYPD investigated 1.3 million and made 791 arrests and 5,482 summonses.²⁷⁷ A 2017 state audit of nightlife noise found that for 85 percent of NYPD responses, either no action was taken or the records did not show how police responded.²⁷⁸

In Boston

Boston sends different noise to different offices - police for parties and car alarms, Inspectional Services for construction, Massport for aircraft, the Public Health Commission for HVAC equipment.¹¹⁵ The full routing table is in The sound of Boston.

Elsewhere in the world: what happens after you complain?

In England and Wales, councils have a legal duty to reasonably investigate complaints of possible statutory nuisance,⁷⁷ but each council sets its own service level, including whether officers come out at night.⁷⁰ If an officer confirms a statutory nuisance, the council must serve an abatement notice.⁷⁰ In the EU, the public must be informed and consulted on noise action plans,²⁵ which is the moment to raise a road or rail corridor that the maps show as loud.

How do people find or make quiet?

What you hear: the drop when you turn off a main road onto a side street, or step into a courtyard.

Distance. Sound from a single source such as a horn falls about 6 dB per doubling of distance. A busy highway acts as a line of sources and falls only about 3 dB per doubling,⁵ or about 4.5 dB over soft ground.⁹ The Federal Highway Administration says traffic noise is usually not serious beyond about 150 m (500 ft) from heavy freeways, or 30 to 60 m (100 to 200 ft) from lightly traveled roads.⁹

Something solid in the way. A barrier that barely breaks the line of sight cuts about 5 dB(A); a good one approaches 10 dB(A). A row of buildings gives about 3 dB(A), plus about 1.5 dB(A) for each additional row. A dense belt of vegetation 5 m tall and 30 m deep can give up to 5 dB(A).⁵ A 10 dB cut sounds roughly half as loud.⁵ This is why a room on the far side of a building, or a street one block back from an arterial, can be noticeably calmer.

Heavy walls, and the bass problem. Walls block sound mostly by mass: transmission loss rises about 6 dB for each doubling of a wall's mass, and falls about 6 dB for each halving of frequency, so bass gets through far more easily than voices. Typical drywall walls also have a resonance dip around 50 to 100 Hz that the standard STC rating can miss. Door seals help with speech, not bass.⁸

Timing. Knowing your local quiet hours tells you when the rules are on your side - for example, power and garden tools are barred in New South Wales from 8 p.m. on weekdays.⁶⁸

Protected quiet. Alongside their action plans, EU member states must select and preserve quiet areas of good acoustic quality.^{76 25} The idea of soundscape - defined in ISO 12913-1 (2014) as the acoustic environment "as perceived or experienced and/or understood by a person or people, in context" - shifts the question from how to remove noise to which sounds are worth keeping.⁹³ Quiet-area mapping and certified quiet parks are covered in Birds, bugs and soundscapes.

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16The sound of Boston

The short version: Boston regulates noise in two layers: City Code limits of 50 dBA overnight and 70 dBA at other times, enforced mostly by police, and a far more technical set of Air Pollution Control Commission rules with limits by zoning district, by octave band and for construction. Massachusetts adds a state policy that treats noise as air pollution and flags anything more than 10 dBA above background, a rule MassDEP proposed revising in March 2026. Who you call depends on the source - police for parties, Inspectional Services for daytime construction, Massport for planes, the Public Health Commission for building equipment. The city's bigger soundmarks - Logan Airport, the Green Line's screech, commuter rail horns, old bells and July 4 cannons - each have their own history and their own rulebook.

What are Boston's noise limits?

What you hear: A party, an air conditioner, a generator, a bar's bass line - anything that is not construction or traffic.

Boston's public summary is short: the city considers anything louder than 50 decibels from 11 p.m. to 7 a.m. unreasonable, and anything louder than 70 decibels unreasonable at any time, except permitted construction.²⁷⁹ Those numbers come from City Code Section 16-26, which the City Council describes in dBA. The Council also notes that in some cases noise "plainly audible" from a set distance violates the code, and that scientific noise measurements are not required before citations may be issued under these provisions. Section 16-27 targets disruptive private gatherings.²⁸⁰

The second layer is the Air Pollution Control Commission (APCC), which writes the city's "Regulations for the Control of Noise." Its zoning-district limits, given as single-number equivalents, are:⁹²

"Daytime" under the APCC rules means 7:00 a.m. to 6:00 p.m. "daily except Sunday." Every other hour, including all of Sunday, falls under the stricter column.⁹²

The APCC rules also set limits for each octave band - a slice of the frequency spectrum - from 31.5 Hz to 8,000 Hz. In a residential district, for example, the limit at 1,000 Hz is 50 dB by day and 40 dB at other times, while at 63 Hz it is 75 dB and 67 dB.⁹² This matters for hum (see The hum). A-weighting (the "A" in dBA) discounts low frequencies, so a rumbling air-handling unit can read modestly in dBA while still breaking a low-band limit.

The APCC exempts intermittent daytime homeowner outdoor equipment, construction (handled separately) and motor vehicles on public ways. It issues permits with conditions, and a variance requires a public hearing and lasts no more than a year.⁹²

What time can construction start in Boston?

What you hear: Backup alarms, saws and excavators, sometimes before you would like.

Regular construction hours in Boston are 7 a.m. to 6 p.m. on weekdays. During those hours, complaints go to Inspectional Services (ISD). After hours, the city suggests checking the after-hours construction permit database on data.boston.gov and calling 311 or ISD if no permit exists. Roadwork is permitted separately, by the Transportation Department and Public Works.²⁷⁹

The APCC sets construction limits measured at the lot line, no closer than 15 m (50 ft) from the nearest active device:⁹²

L10 is the level exceeded 10 percent of the time - a measure of the louder moments rather than the average. Street excavation, grading, repair and utility equipment may not exceed 86 dBA at 15 m (50 ft), and emergency utility work has 24 hours to come into compliance. Impact devices - pile drivers, paving breakers, jackhammers - are exempt from both of those limits.⁹²

Residential trash collection starts at 6 a.m. The city says it cannot set commercial waste pickup hours in business, commercial or industrial zones because of state law, M.G.L. c. 111 s. 31A.²⁷⁹

What is the Massachusetts 10 dBA rule?

What you hear: A new compressor, fan or substation that seems loud mainly because the place used to be quiet.

Massachusetts regulates noise as a form of air pollution under M.G.L. c. 111 and 310 CMR 7.00. The specific rule, 310 CMR 7.10, prohibits unnecessary or excessive noise from man-made sources.²⁸¹ MassDEP's 1990 Noise Policy - guidance, not regulation - says a source violates 7.10 if it raises the sound level 10 dBA above ambient, or creates a pure tone condition (a noise dominated by one pitch), measured at the property line and at the nearest receptor. "Ambient" means L90, the A-weighted level exceeded 90 percent of the time during equipment operating hours. Measured in the quietest periods, it can be as low as 20 to 30 dBA in rural areas.²⁸¹

The same machine can be legal in a loud city and illegal in a quiet town. On March 2, 2026, MassDEP released a discussion document proposing changes: a 40 dBA level presumed acceptable at sensitive receptors and "very quiet areas"; measuring at receptors such as homes, schools, hospitals and elder care rather than property lines; and averaging the lowest hourly L90 values instead of using the single lowest one. The comment deadline was extended to 5 p.m. on April 30, 2026. The review was prompted partly by March 29, 2024 recommendations from the state's Commission on Energy Infrastructure Siting and Permitting.²⁸¹ As of October 2026, we found no final revised policy.

State policy applies in Boston alongside the APCC limits.

Who regulates leaf blowers around Boston?

What you hear: A two-stroke whine on a Saturday morning, a block over.

No Boston-specific leaf blower ordinance turned up in our sources; the APCC exempts intermittent daytime homeowner equipment from its zoning limits.⁹² The rules are in neighboring towns.

Brookline bans gas blowers January 1 to March 14 and May 16 to September 30, and allows them March 15 to May 15 and October 1 to December 31. Hours are 8 a.m. to 8 p.m. on weekdays and 9 a.m. to 6 p.m. on weekends and holidays; electric blowers are allowed year-round in those hours. Any blower must be rated no louder than 67 dBA at 50 ft, shown by a manufacturer or DPW sticker. Landscapers need a $25 annual permit, and fines escalate from a warning to $50, $100 and $150 per calendar year.²⁸²

Cambridge moved from seasonal limits to a gas ban in stages. As of November 2023, it limited blowers to March 15 to June 15 and September 15 to December 31, with commercial licenses, and was considering a ban on handheld and backpack gas blowers - residents by March 2025, businesses by 2026 - with wheeled models exempt. Its ordinance committee voted 6-0 for the 2026 date.²⁸³

In that debate, supporters, including Cambridge Councilor Patricia Nolan, cited the health of residents and workers; the Globe cited a 2021 California Air Resources Board estimate that an hour of commercial blower use pollutes about as much as driving roughly 1,100 miles. Opponents, including a Cambridge landscaping company owner, said electric blowers are weaker, heavier and battery-limited, and MIT officials asked for the later 2026 deadline so they could replace equipment.²⁸³

The City Council passed the updated ordinance in December 2023. Since March 15, 2025, property owners have not been allowed to use gas blowers on their own property; commercial operators, owners of adjoining parcels totaling two or more acres, city employees and city contractors could keep using them until March 15, 2026.¹⁹⁸ The city's leaf blower page says that since then those remaining users are also limited to electric blowers.¹⁹⁹ A License Commission summary revised February 13, 2026, says all gas leaf blowers "have been banned," but still lists narrow exceptions for municipal contractors: residential street cleaning (while the city does not tow for it), parcels of one acre or larger, and emergencies. The two city sources differ on that point. The summary also caps electric blowers at 65 dBA, as rated by the manufacturer under the ANSI standard.²⁰⁰

As of October 2026, Cambridge allows blowing March 15 to June 15 and September 15 to December 31, from 8 a.m. to 5 p.m. on weekdays and 9 a.m. to 5 p.m. on Saturdays, and not on Sundays or legal holidays, except for set afternoon hours on Indigenous Peoples' Day and Veterans Day. Commercial operators need a permit from the Board of License Commissioners, and operating without one carries a $300 fine.¹⁹⁹

Nearby, as of the Globe's November 2023 report, Arlington's ban was scheduled to take effect for businesses in 2025 and residents in 2026, and Belmont and Lexington had similar measures.²⁸³ Why gas blowers carry so far, and the wider ban debate, are in Construction and leaf blowers.

Who do I call about noise in Boston?

What you hear: Whatever it is, at 1 a.m., and you want it handled by the right office.

Boston splits noise reporting by source:²⁷⁹²⁸⁰

311 is a general channel too. A 2021 NBC Boston analysis of more than 375,000 311 reports since early 2020 found Public Works received roughly half of them; noise was not broken out.²⁸⁴

Published counts of noise in Boston's 311 data are scattered. WBUR's year-end tally of 2024 requests found 668 about loud parties, with October the busiest month at 128.²⁸⁵ For the pandemic years, Boston Magazine reported in November 2021 that 311 entries containing the word "noise" were 32 percent higher in 2020 than in 2019, and that the city counted a rise of about 5,500 percent in fireworks complaints over the previous year.²⁸⁶

What happened at the July 2026 City Council noise hearing?

In July 2026, nine Boston city councilors filed a hearing order, dated July 22, on the city's response to noise complaints. It asks for complaint counts, response times, citations issued, the availability of sound meters, and geographic disparities, and cites complaints particularly from District 7 that calls often produce little visible enforcement.²⁸⁰ On July 24, 2026, the Council adopted a resolution urging a stronger response to noise complaints.²⁸⁷

As of October 2026, we found no published answer to the data the order requested.

Why are there so many planes over Cambridge and Somerville?

What you hear: Jet after jet on what sounds like the same line in the sky, every few minutes.

In 2014, new satellite-based RNAV (area navigation) procedures took effect at Logan, following a 2013 FAA environmental assessment. Because RNAV paths are precise, departures from Runway 33L concentrated over north and west Cambridge.¹⁷² Precision that keeps planes tidy for air traffic control also puts them over the same homes, flight after flight.

In October 2016, the FAA and Massport signed an agreement to test ways of reducing overflight noise from these procedures. The study areas included Runway 33L departures (Arlington, Belmont, Cambridge, Watertown), Runway 27 arrivals, over-water 22R/22L departures (South Boston, Hull) and a curved Runway 4R approach (Milton, Dorchester).²⁸⁸

MIT's International Center for Air Transportation, led by Professor John Hansman, worked on the study for six years. Across two phases it sent four procedures to the FAA, and it found over-water routing the most effective strategy. A curved RNP (Required Navigation Performance) approach to Runway 33L was implemented in 2021, estimated to remove 2,954 people from exposure to aircraft noise above 60 dB. An over-water RNAV approach to Runway 22L was planned for initial use in 2024, estimated to cut by 131,892 the number of people exposed to 50 or more daily overflights above 60 dB.²⁸⁹

The departure side went differently. In 2021, MIT proposed a modified 33L takeoff path over central Somerville and Porter Square. Cambridge and most communities on Massport's Community Advisory Committee (CAC) voted against recommending it. Cambridge says the FAA has not announced next steps on it, and describes the study as complete, with the FAA implementing a few of its recommendations.¹⁷²

The FAA's Boston community engagement page says the second block of procedures, approved by the Massport CAC on December 9, 2021, was published on November 30, 2023. For the over-water RNAV approach to Runway 22L, it says the CAC requested a 12-month operational test, that testing was completed, and that MIT gave the noise measurements to the CAC for review. As of October 2026, the page reports no results and no figures on how often the approach is flown.²⁹⁰

How do I complain about Logan Airport noise?

The CAC was created by the state legislature to advise Massport¹⁷² and represents 35 communities.²⁹¹ Cambridge commented in 2023 on the FAA's Noise Policy Review, which covers the DNL (day-night average sound level) metric and its 65 dB threshold.¹⁷² How DNL works is explained in Planes and helicopters.

For individual complaints:¹⁷²

• Massport Noise Complaint Line: 617-561-3333, staffed 6 a.m. to 5 p.m. on business days, automated after hours.
• Online portal: requires registration; responses typically take three to four weeks; several emails in a short period count as one complaint.
• Flight Monitor: Massport's near-live map of flight tracks.
• FAA New England Aviation Noise Ombudsman: 9-ane-noise@faa.gov, 781-238-7400.

Massport began publishing a "Fly Quiet Report" with the first quarter of 2019.¹⁷² For the tools hobbyists use to identify a plane overhead, see The Airwaves.

Does Massport soundproof homes?

Massport's residential sound insulation program began in 1985, is funded by the FAA, and has insulated more than 11,000 homes. Homes treated from 1984 to 1993 were not eligible to be redone until Massport asked the FAA in January 2020 to reconsider "a narrow set of eligible homes with the highest noise exposure"; Winthrop's Point Shirley was expected to benefit.²⁹¹ Logan has also soundproofed the schools most affected by aircraft noise.²⁹²

Why does the Green Line screech?

What you hear: A long, high-pitched squeal as a trolley rounds a tight underground curve.

The station riders mention most is Boylston, where inbound trains turn from Boylston Street onto Tremont at close to 90 degrees. Boylston and Park Street opened in 1897. According to acoustical consultant Jeff Zapfe of Acentech, the wheel sticks and slips on the rail, vibrates and radiates the squeal - this is wheel squeal. The curve "was made for trains that don't exist anymore," an MBTA light rail maintenance official said in 2017. At the time the MBTA had 13 greaser units on the Green Line with six more planned, and had fitted flange lubricators on all newer Green Line trains.¹⁵⁷

In 2022, MBTA chief engineer Eric Stoothoff added that restraining rails on tight curves rub the backs of the wheels. The agency lubricates tracks and wheels, and Stoothoff said future Green Line planning at Boylston could change the track geometry; GBH reported a fix would likely take until at least the end of the decade or the start of the next.²⁹³

Why do commuter rail trains honk so much?

What you hear: Long, long, short, long at every grade crossing.

That pattern is federal. Under the Federal Railroad Administration's train horn rule, in effect since 2005, horns must sound at a minimum of 96 dB and a maximum of 110 dB, starting 15 to 20 seconds before a public crossing (and no more than a quarter mile ahead at speeds over 45 mph). A quiet zone - at least half a mile of track where crossings have extra safety measures - lets trains skip routine horns.²⁹⁴

In Massachusetts, 28 municipalities had FRA-approved quiet zones as of the CommonWealth Beacon's reporting (October 2021, updated September 2023): six "new" zones (Cambridge, Hingham, Lincoln, Revere, Rowley, Waltham) and 22 that predate the rule. Chelsea lost its pre-rule status in 2020 and, per that report, was spending $2.5 million to comply. MBTA General Manager Steve Poftak wrote in 2019 that quiet zones "compromise the safety" of employees, customers and the public.²⁹⁵

Cambridge's Sherman Street crossing shows how fragile a quiet zone can be. Horns resumed around June 29, 2018, after a Keolis audit found no quiet zone designation. The city filed a Notice of Intent on July 16, 2018, and the FRA approved an alternative safety measure on November 26, 2019.²⁹⁶

What did the Big Dig teach about construction noise?

What you hear: Nothing now. For years, it was the loudest project in the city.

The Central Artery/Tunnel Project wrote one of the most detailed construction noise specifications in the US, Section 721.560. It treated Sundays and federal holidays as nighttime and divided the rest into daytime (7 a.m.-6 p.m.), evening (6-10 p.m.) and nighttime (10 p.m.-7 a.m.).²⁹⁷ Limits at noise-sensitive lot lines (dBA, slow response) were tied to background:²⁹⁷

Each machine also had an emission limit, Lmax at 50 ft: 85 dBA for excavators, dozers, cranes and jackhammers; 90 for concrete saws and hoe rams; 95 for pile drivers; 82 for generators over 25 kVA; 73 for welders; 55 for pickups. Contractors measured weekly at each sensitive location against a 24-hour baseline.²⁹⁷ Mitigation included barriers rated STC-30 or better with an absorptive liner, ambient-sensitive backup alarms no more than 5 dBA above background, no impact pile driving from 6 p.m. to 7 a.m., and no hoe rams or jackhammers from 10 p.m. to 7 a.m. without approval.²⁹⁷

The data outlived the project. The FHWA's Roadway Construction Noise Model is "based on the noise calculations and extensive construction noise data compiled for the CA/T Project." Its guide notes that impact pile drivers, specified at Lmax 95 dBA, actually measured 101 dBA at 50 ft across 11 samples.²⁹⁸ The FHWA cites the 2002 Massachusetts Turnpike Authority version of the spec and Erich Thalheimer's 2000 paper on the program.²⁹⁹

When do Boston's church bells ring?

What you hear: A tumbling, unmelodic cascade of bells on a Sunday late morning.

That is likely change ringing - tuned bells rung in mathematical sequences rather than tunes - from Old North Church. Its eight bells were installed in 1745; the treble is inscribed 1744 with the church's claim, "We are the first ring of bells cast for the British Empire in North America." The treble weighs about 620 lbs (280 kg) and the tenor about 1,500 lbs (680 kg). Paul Revere rang them from 1750, at about age 15. They ring on Sundays after the 11 a.m. service and on holidays such as July 4, with full peals about twice a year.³⁰⁰ The bells were cast by Abel Rudhall of Gloucester, England, and are rung by the MIT Guild of Bellringers.³⁰¹

Revere recast the King's Chapel bell in 1814, his largest and last, and an 1801 Revere bell was installed at Old South Meeting House in 2011. Park Street Church's bells (2021) chime Westminster quarters, and the Mother Church of Christian Science has an 18-bell carillon (1984).³⁰¹

Are the July 4 cannons real?

Yes. At the end of Tchaikovsky's 1812 Overture during the Boston Pops July 4 concert, a small squad of Massachusetts National Guard soldiers from the 101st Field Artillery fires three howitzers aimed toward the Charles River for about 20 seconds.³⁰²

Does Boston Harbor still have foghorns?

What you hear: A single horn blast out on the water, repeating on a slow clock.

Boston Light, first lit September 14, 1716, received a fog cannon in 1719 at keeper John Hayes's request. MIT students tested foghorns there in 1893. The light was automated in 1998, and its fog signal is listed as one horn blast every 30 seconds.³⁰³ Graves Light, farther out, had a bell buoy from 1855; a 1905 Globe description called the sounds of its successor, a larger air-driven buoy, "the most weirdly mournful and bloodchilling." A Daboll trumpet went into service there on November 23, 1905. The light has been solar-powered since 2001, with an automated foghorn.³⁰⁴

What is the loudest neighborhood in Boston?

The main academic sound map of Boston is Erica Walker's. She bicycled the city recording at roughly 400 to 450 sampling sites, including low-frequency sound and infrasound; in 2015 she reported East Boston and Savin Hill tied as the loudest daytime neighborhoods.³⁰⁵ Her 2016 conference paper found that low-frequency noise dominates the urban environment, and that time of day, land use, proximity to major roads, bus and train routes, hospitals and building density all significantly affected median levels. Residents' perception maps matched the measured hot spots near transit.³⁰⁶

Boston University's Community Noise Lab launched in fall 2019 with an app, NoiseScore, that pairs readings with how a sound makes people feel on a live map. Early work covered Fenway (summer concerts and construction), Mission Hill (sirens and helicopters near Longwood), East Boston and Chelsea.³⁰⁷

Elsewhere in the world

Many US cities use a single dBA limit at the property line; Boston's octave-band limits add a check on low-frequency hum. Massachusetts' "relative to background" rule differs from the absolute limits most cities use, and the 2026 revision proposal aims at the gap that creates between rural and urban places.²⁸¹ US airport noise is judged against the FAA's DNL 65 dB line, a policy Cambridge asked the FAA in 2023 to revisit with stronger health protections.¹⁷²

Report an error in this section

17Test yourself

The short version: Sixteen questions drawn from this guide, from easy to surprising. Each answer explains itself and links to the section that covers it.

Report an error in this section

18The glossary

The short version: Every term of art in this guide in plain words, searchable and sorted by topic. If a word on a noise map, an airport report, a hearing test or a city notice stopped you, it should be here.

Report an error in this section

19Where to go next

The short version: The best places to keep going, none of them ours: the health agencies, regulators, researchers and sound projects behind this guide.

20Open questions and known gaps

The short version: What we looked for and could not pin down well enough to print. If you can source any of it, the corrections desk below wants to hear from you.

21Corrections and updates

The short version: This guide will have mistakes in it, and the people who know best are the ones who run these systems every day. If something here is wrong, out of date or missing credit, tell us and we will fix it and log the change below with the date.