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On Wind Turbine Noise and Air Pressure Pulses 

Author:  | Noise, Regulations

The von Trapp family came to Vermont because it reminded them of Austria, where “the hills are alive with the sounds of music”. Those sounds will soon be replaced by the health-damaging infrasound and low frequency noise from 3 MW wind turbines on 2,000-ft high ridge lines, courtesy of GMP/Gaz-Metro-Canada.

GMP’s 21 wind turbines of the Lowell Mountain facility will emit various noises, such as:

  • machinery noise in the nacelle
  • rhythmic/pulsating, trailing-edge noise from the blades (“blade swish”) as they slice through the air at up to 200 mph- irregular, low frequency noise (LFN) and infrasound from the blades due to in-flow air turbulence
  • LFN and infrasound at the blade-tower-passage frequency and its harmonics.

Infrasound consists of air pressure pulsations, less than 20 Hz; not audible, but felt; usually not measured by acoustics engineers; more or less ignored by state regulators and state noise codes, mainly because wind energy promoters (vendors, project developers, financial types with tax-shelter schemes for the top 1% of households, legislators getting “campaign” contributions, etc.) have been saying wind energy is “clean and green” and LFN and infrasound are a non-issue.

At 350 m (1,148 ft) from a utility-scale wind turbine, the audible sound emitted by:

  • a well-behaving wind turbine with no in-flow turbulence and low wind shear is about 35 dB(A); often during daytime when the sun is warming the ground and air.
  • a badly-behaving wind turbine with in-flow turbulence and/or high wind shear is up to 55 dB(A); often during nighttime when a stable atmosphere forms.

This compares with rural nighttime noise of 20-40 dB(A) and urban residential nighttime noise of 58-62 dB(A).

The wind speeds and directions upstream of a wind turbine vary due to terrain effects, such as hilliness and ridge lines, objects on the surface of the terrain, such as buildings and trees, daytime thermal effects and upwind wind turbines.

During daytime, as the 3-bladed rotor turns, it encounters air at various speeds and directions which produces a combination of sound effects, i.e., rhythmic/pulsating blade swish about 3 dB(A) above the steady aerodynamic noise, and a steady rhythm of LFN and infrasound.

Note:  Doubling the sound power, watt, increases the sound power level by 3 dB. Doubling the sound pressure, micropascal, increases the sound pressure level, SPL, by 6 dB.

For example: If at 800 uPa (micropascal) the SPL = 20 log (800/20) = 32 dB, at 1600 uPa it is 38 dB, and at 3200 uPa it is 44 dB.


During nighttime, air speeds and directions, not influenced by daytime thermal effects, become more varied, the atmosphere becomes more stratified and background noise is less causing the various sound effects (aerodynamic noise, rhythmic/pulsating noises, rhythmic LFN and infrasound) to be noticeably more intense than during the daytime. The daytime blade swish noise often becomes a nighttime clapping, beating, or thumping noise. As the 3-bladed rotor turns at 15 to 20 rpm at greater wind speeds, a blade reaches the top about 45 to 60 times per minute, or 0.75 to 1.0 Hz. At lesser wind speeds the frequencies are less.

The infrasound has audible components (20 to 500 Hz with peak amplitudes at about 200 to 500 Hz) and inaudible components (0 to 20 Hz with peak amplitudes at about 0.75 to 1.0 Hz). The infrasound travels great distances, a mile of more, for large, utility-size wind turbines.

The wind speeds and directions downstream of a wind turbine are similar to the vortices leaving the ends of airplane wings, except they all rotate in the same direction. When the wind direction aligns with the ridge direction of the wind turbines, the downwind turbines will have a degraded performance of up to 20 to 30 percent, i.e., a reduced CF, due to wake turbulence, and they will be noisier, and they will have increased wear and tear.






Government Noise Codes

Traditionally, state and local government codes dealt mostly with measured sound values that are weighed (adjusted) using the A scale which covers most of the audible frequencies. The A scale corrects dB measurements according to the sensitivity of human hearing. It should not be used for frequencies less than 200 HZ, as the low frequency noise (LFN) and infrasound would be “weighed” out.

The following scales should be used to properly weigh all frequencies, especially those less than 20 Hz that are emitted by wind turbines:

  • Most audible noises in the range of 200-20,000 Hz; dB weighed with the A scale, dB(A).
  • LFN, in the range of 20-200 Hz; dB weighed with the C scale, dB(C).
  • Infrasound less than 20 Hz; dB weighed with the G scale, dB(G). (The instrumentation to quantify infrasound frequencies and amplitudes is expensive and the values obtained vary with the method and instruments used. Applying the G scale to such values may not be meaningful.)

The human ear can hear LFN at 95 dB(G) levels, the inner ear is sensitive to LFN at 65 dB(G) levels. Audible thresholds for perception, ToP, of 95 dB(G) represent the median response to a steady pure tone in a laboratory environment.

If a person is more sensitive to LFN and infrasound, say at the 10% boundary, the ToP may be as low as 85 dB(G) for a steady pure tone. The ToP will also be lower with multiple tones between 0 and 100 Hz that rapidly modulate in amplitude and frequency, as with wind turbine noise.


Professional acoustical engineers know the government codes, the outcome government regulators are expected to hear and conduct their tests according to standard procedures using mostly the A scale. Wind turbine vendors report sound levels adjusted to the A scale and everyone is satisfied. The LFN and infrasound are usually not covered by government codes.

According to the US EPA, noise levels above 45 dB(A) disturb sleep and most people cannot sleep at noise levels above 70 dB(A).

In Massachusetts, noise is considered pollution if it exceeds the ambient noise level by 10 dB(A). The Department of Environmental Protection, MassDEP, measures noise levels at the complainant’s location and at other nearby locations that may be affected, such as residences and/or buildings with other sensitive receptors. If the noise level at a sensitive receptor’s location is more than 10 dB(A) above ambient, MassDEP requires the noise source to mitigate its impact. The LFN and infrasound are not covered.


In Michigan, the Centerville Township, after 4 years of study, developed and approved a zoning ordinance for commercial wind energy systems. It is strict and comprehensive and should serve as a model for other government entities.

Audible Noise Standard

From 6:00 a.m. until 10:00 p.m., for wind speeds from cut-in to rated-output of the wind turbine facility, the noise level due to the wind turbine facility at the property line closest and at locations within 1 mile of the wind turbine facility shall not exceed the greater of 35 dB(A), or the established outdoor background sound level by more than 5 dB(A).

From 10:00 p.m. until 6:00 a.m., the noise level due to the wind turbine facility at the property line closest and at locations within 1 mile of the wind turbine facility shall not exceed the established outdoor background sound level by more than 3 dB(A). Background sound level shall be established separately for daytime (6:00 a.m.–10:00 p.m.) and for nighttime (10:00 p.m.–6:00 a.m.) values.

LFN or Infrasound

No LFN or infrasound from wind turbine facility operations shall be created which causes the noise level both within the project boundary and a 1 mile radius beyond the project boundary to exceed the following limits:

Octave Band Center Frequency, Hz   Sound Pressure Level (dB-SPL)
1-2   70
16   60
31.5   65
63   57
125   50
250   47

Tonality and/or Repetitive, Impulsive Tone Penalty

In the event the audible noise due to wind turbine facility operations exhibits tonality, contains a pure tone and/or repetitive, impulsive noise, the Audible Noise Standard shall be reduced by a total of 5 dB(A).


In Maine, codes require noise levels not to exceed the one-hour average daytime limit (between 7 a.m. and 7 p.m.) of 55 dB(A), and one-hour nighttime limit (between 7 p.m. and 7 a.m.) of 42 dB(A), as measured within 500 feet from a residence, seasonal camp or business at “protected locations”, and 55 dB(A) 24 hours of the day at greater than 500 feet from a residence, seasonal camp or business at “protected locations”, and 75 dB(A) at the wind turbine project boundary. The LFN and infrasound are not covered.



Maine Department of Environmental Protection 06-096 CMR c. 375.10.


Till now, 32 Maine towns have passed their own wind facility ordinances that are stricter than the state ordinance, because they do not trust the state to protect the public safety, health, property values and welfare of the people. This site provides the URLs of the text of the wind ordinances of 12 Maine towns. Vermont towns should get copies of them and use them as a guide to write their own ordinances before it is too late.


In Vermont, codes require nighttime noise levels not to exceed 40 dB(A) as measured at the exterior of a dwelling facade and averaged over a 12-month exposure, the same as the recommendations of the 2009 World Health Organization report that mostly cover road noise, air traffic, and community noise and do not mention wind turbine noise. LFN and infrasound are not covered. The Vermont code does not protect the public health, safety and welfare; it is a wind turbine vendor’s dream come true.

dB values should be measured “at the property line” to ensure people can enjoy their entire property and should not be “averaged over a 12-month period” which would average higher noise levels at higher wind speeds occurring mostly during nighttimes with lower noise levels at lower wind speeds occurring mostly during daytimes.



Wind Turbine Noise Annoyance

On an annoyance scale that is based on interviews of people who live near wind turbines, airports, railroads and highways, wind turbine noise is much more annoying at less than 40 dB(A), than the noise from aircraft, highway and rail traffic at less than 70 dB(A).

This additional annoyance is due to the LFN and infrasound emitted by wind turbines. The measured wind turbine noise appears to be benign and within code, but the annoying/unhealthy LFN and infrasound were filtered out by the A scale weighing.


Health Impacts

At less than 20 Hz (infrasound) and above 20,000 Hz (ultrasound) most people do not “hear” noise, but a person’s ears and body are sensitive to infrasound which cause nausea, headaches, insomnia, elevated blood pressure, palpitations, tinnitus, imbalance, dizziness, lack of concentration, moodiness, irritability, anxiety, etc., in SOME people who live about 1/2 mile or less from large, say 1.0 MW, utility-size wind turbines. Infrasound also has potential to harm wildlife and livestock. Little is known about the issue. But there is anecdotal evidence indicating problems. These symptoms are collectively known as “Wind Turbine Syndrome”.

These symptoms occur because the natural frequencies of the internal human and animal organs are in the same frequency range, i.e., 4 to 8 Hz, as those of house walls and floors. Floor resonance can cause the internal organs of the occupants to resonate resulting in an uneasy, irritating feeling. The infrasound is often amplified indoors due to resonating of house walls and floors.

Most peoples’ heart beat is less than 1.25 Hz, or a 75 pulse rate. People who live close to large wind turbines in Falmouth, MA, Ontario, Australia, etc., have complained about feeling internal pressures and having heart troubles and other symptoms which they did not have before the wind turbines were installed.

The symptoms mostly disappear after people move away and reappear after they move back. After many complaints over a long period of time, the Falmouth ruling council finally slowed down the wind turbines at greater wind speeds by partially feathering the blades.

Larger Wind Turbines, Stronger Vibrations

The symptoms studied up till now typically are from exposure to the LFN and infrasound from smaller wind turbines, say up to 2 MW, with 290 ft diameter rotors, as on Lempster Mountain, NH.

The 3 MW Lowell Mountain wind turbines, with 367.5 ft diameter rotors, on 275.6 ft masts, on 2,600 ft high ridge lines, will have greater impacts over larger areas. See website.


The relative amount of LFN is greater for large turbines (2.3–3.6 MW) than for small turbines (less than 2 MW), i.e., the noise from larger wind turbines affects a larger area than from smaller wind turbines. The difference is statistically significant for one-third-octave bands in the frequency range 63–250 Hz.

During the day, ambient audible noise (background noise) in rural areas is much greater than at night, whereas, because of greater nighttime wind speeds, the wind turbine noise is greater at night than during the day. The result is rural people notice audible wind turbine noise much more at night than during the day. Wind turbine promoters arrange field trips for legislators and the public during the day from May-September when wind speeds and noise are minimal.

Dealing With Complaints

Many people living near wind turbines complain about sleep-disturbing nighttime noises that upset their lives to such an extent that their houses are bought by wind turbine owners after they sign gag orders.

As more and larger wind turbines are built near where people work, study, play, etc., the complaints will just multiply, until political pressures restrict the siting of wind turbine projects without suitable buffer zones, or require siting them offshore.

Dismissing the effects as mostly psychological and saying the physical effects are due to something else is not an option; there are just too many people, in too many geographical areas, living too near large wind turbines, with too many complaints. It is better to deal with the problem.

One way to deal with it is to have sufficient distance between people’s houses and utility-scale wind turbines to ensure people are not disturbed by noise and infrasound. Various studies show people living in flat terrain with wind turbines should be at least 1.25 miles (2 km) from such wind turbines. People living in mountainous terrain with wind turbines on ridge lines should be at least 2 miles (3.2 km) from such wind turbines. Such distance standards are becoming more prevalent in Europe, Australia, etc.

Professional acoustical engineers Rick James and George Kamperman have extensively studied wind turbine noise. They recommend a noise limit AT THE PROPERTY LINE for:- Audible noise: 35 dB(A) or no more than 5 dB(A) above the pre-construction ambient dB(A) level, whichever is lower- LFN: 50 dB(C) or no more than 20 dB(C) above the pre-construction ambient dB(C) level, whichever is lower


Vestas is concerned its 3 MW turbine will not meet stricter noise codes and has actively opposed noise code changes in Denmark, because it fears such changes will set a precedent for changing noise codes throughout the world, thereby adversely affecting 3 MW turbine sales. Other wind energy promoters are also actively opposing noise code changes.

After numerous complaints from people near wind turbine facilities, the Maine Board of Environmental Protection has finally adopted by a 5-4 vote new rules that lower the maximum allowable sound levels emitted by wind farms from 45 dB(A) to 42 dB(A), between 7 p.m. and 7 a.m., as measured from houses and other “protected locations” within one mile of the turbines; a good step in the right direction, but inadequate for rural settings.

Vermont state officials are rushing to have as many ridge line wind facilities built as possible before various federal subsidies expire.

Because of this rushing, they have not heeded, or played down, or dismissed, the environmental concerns of professional testifiers and the complaints from people who live near the Lowell Mountain wind turbine facility. They likely will also not heed the complaints from the fauna and flora currently inhabiting this pristine ridge line.

Because of them, Vermonters are in danger of losing an international reputation of being preservers of their environment and in danger of losing a part of their soul.

By means of various rigged polls to provide CYA for legislators and by means of PR campaigns by wind energy promoters, including foreign companies selling wind turbines, Vermonters were swayed/bamboozled to be in favor of “clean and green” wind energy on ridge lines. However, after they saw the environmental destruction on the 2,600 ft-high Lowell Mountain ridge line, they quickly sobered up.

What makes wind energy even less attractive is that some recent studies show CO2 emission reductions due to wind energy are not anywhere near to what is claimed by promoters. These studies are based on 1/4-hour and 1-hour grid operations data.

Because wind energy is variable and intermittent, it requires backup by quick-ramping, open cycle gas turbine generators that ramp up when wind energy ebbs and ramp down when wind energy surges which occurs at least 100 times per day. Such part-load-ramping operation is inefficient and requires extra fuel/kWh and emits extra CO2/kWh. The extras mostly offset what wind energy was meant to reduce, as proven by analysis of the Eirgrid, Texas and Colorado grid operations data.







Vermonters may want renewable energy, but NOT AT ANY COST, and they certainly do not like to be rushed, forever ruin parts of their state, to beat arbitrary subsidy deadlines for RE projects that will quickly enrich the politically-well-connected top 1% of households at the expense of already-struggling households and businesses in a nearly zero-growth economy.





















[via theenergycollective.com]

This material is the work of the author(s) indicated. Any opinions expressed in it are not necessarily those of National Wind Watch.

The copyright of this material resides with the author(s). As part of its noncommercial educational effort to present the environmental, social, scientific, and economic issues of large-scale wind power development to a global audience seeking such information, National Wind Watch endeavors to observe “fair use” as provided for in section 107 of U.S. Copyright Law and similar “fair dealing” provisions of the copyright laws of other nations. Queries e-mail.

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