Wind turbines, infrasound, and health effects

Nov 8, 2010


“Infrasound: Your ears ‘hear’ it but they don’t tell your brain”

Alec Salt, PhD, Department of Otolaryngology, Washington University School of Medicine, St. Louis, Missouri, USA, at the “Symposium on Adverse Health Effects of Industrial Wind Turbines,” Picton, Ontario, October 29-31, 2010.  (See the Cochlear Fluids Research Laboratory site, and “Responses of the Ear to Infrasound and Wind Turbines.”


“Physiologic pathway exists for infrasound at levels that are not heard to affect the brain. The idea that infrasound effects can be dismissed because they are inaudible is incorrect.”

“A-weighted measurements tell you NOTHING about infrasound content.”

“A-weighted spectra totally misrepresent the effects of wind turbine noise (that includes infrasound components) on the ear.”

“A-weighted level readings (e.g., 42 dBA) are totally meaningless for assessing whether turbine noise is affecting the ear.”

Click here to download a PDF of Dr. Salt’s PowerPoint slides, from which the following text was taken.

Wind turbines generate infrasound.

Wind turbine infrasound is at levels that cannot be heard.

Widely cited interpretations:

  • “If you cannot hear a sound … it does not affect you”—Leventhall G. What is infrasound? Progress in Biophysics and Molecular Biology 2007; 93:130–137
  • “Infrasound is negligible”—DELTA. Low Frequency Noise from Large Wind Turbines 2008
  • “Infrasound … is below the audible threshold and of no consequence”—Leventhall G. Canadian Acoustics 2006; 34:29-36.

This logic seems to be applied only to hearing. Consider other senses:

  • Taste: If you can’t taste it, it can’t affect you? Can you taste salmonella?
  • Smell: If you can’t smell it, it can’t affect you? Try breathing pure CO or CO₂
  • Sight: If you can’t see it, it can’t affect you? Photokeratitis, “snow blindness”, “welder’s flash”, cataracts, sunburn: Ultraviolet (UV) light is invisible; even though you can’t see it, UV does affect you. UV can harm you.

“If you can’t hear it, it can’t affect you” is only true:

  • if no other part of the ear is more sensitive than hearing, and
  • if no other part of the body is more sensitive than hearing …
  • and I will show this is not true.

Infrasound at moderate levels is detected by the ear.

Infrasound at levels generated by turbines affect the ear.

Vibrations cause a bending of the ear’s sensory hairs. The inner hair cells are connected to auditory (type I) nerve fibers that send signals to the brain. You “hear” with your inner hair cells.

Inner (IHC) and outer (OHC) hair cells respond differently as sound frequency is changed. IHC respond to velocity. OHC respond to displacement. OHC respond at approximately 40 dB below IHC sensitivity at 2 Hz.

Outer hair cells will be stimulated by wind turbine noise.  (See graph, below.)

Outer hair cells do not just detect sound:

For low-amplitude high frequencies, OHC elongate when hairs are bent outwards, which makes stimulus greater for IHC (amplifies signal).

Amplifier becomes less effective (less necessary) for higher level sounds, ineffective about 40 dB above threshold (Reichenbach T, Hudspeth AJ. Proc Natl Acad Sci U.S.A. 2010)

High-Frequency stimulus: OHC elongate; Vibration amplitude at the IHC is amplified.

At very low frequencies, we know that bending the hairs laterally causes OHC to contract.

Infrasound stimulus: OHC contract; Vibration amplitude at the IHC is reduced.

OHC are detecting low-level infrasound and actively canceling it for the IHC.

Physiologic pathway exists for infrasound at levels that are not heard to affect the brain. The idea that infrasound effects can be dismissed because they are inaudible is incorrect.

Infrasound => OHC => (via type II nerve fibers) subconscious brain: ear fullness, ear pressure, discomfort, alerting/sleep disturbance

A-weighting corrects a sound measurement to represent what is heard, based on the human audibility (40 phon) curve. At 1 Hz, −148 dB correction, equivalent to dividing by 25 million.

Effect of A-weighting wind turbine noise: Massive (140 dB) de-emphasis of infrasound component. A-weighting may represent what you hear—but hearing does not give a reliable indication of whether the infrasound is affecting your ears.

“A-weighting” principle applied to UV light is equivalent to adjusting sunlight spectrum for what is visible and then saying: “There is nothing here that can harm you. You don’t need sunscreen. You don’t need sunglasses. Go spend all day laying out in the sun.” This approach isn’t rational when applied to light, so why do we accept similar logic applied to sound?

Measuring visible light (e.g., photographs) tells you NOTHING about UV content. Similarly, A-weighted measurements tell you NOTHING about infrasound content.

A-weighted spectra totally misrepresent the effects of wind turbine noise (that includes infrasound components) on the ear.

A-weighted level readings (e.g., 42 dBA) are totally meaningless for assessing whether turbine noise is affecting the ear.

Documenting Wind Turbine Sound

  • Most video cameras do not record the infrasound component of wind turbine noise.
  • Speaker systems in TVs and computers cannot play back the infrasound component.
  • Even if they did—you can’t hear it!
  • Video recordings of wind turbines give no indication of the infrasound level being produced.
  • Infrasound can only be measured with specialized instrumentation capable of detecting sounds down to approximately 1 Hz.

G-weighting weights infrasound components (excluding higher frequencies) according to human sensitivity curve.

G-weighted turbine measurements: For most of these conditions, the ear will be stimulated by the turbine noise. (Jakobsen J. Infrasound emission from wind turbines. Journal of Low Frequency Noise Vibration and Active Control 2005; 24:145-155.)

Other ways that infrasound could affect the ear:

Stimulation of vestibular hair cells (saccule, utricle).

  • Vestibular hair cells are “tuned” to infrasonic frequencies.
  • No-one has ever measured sensitivity to acoustic infrasound.
  • Symptoms: unsteadiness, queasiness

Disturbance of inner ear fluids (e.g. endolymph volume).

  • Low-frequency sound at non-damaging levels induces endolymphatic hydrops (a swelling of one of the fluid spaces).
  • Infrasound does affect endolymph volume—it is the basis of a treatment for hydrops (Ménière’s disease).
  • No one has ever measured what level of infrasound causes hydrops.
  • Symptoms: ear fullness, unsteadiness, tinnitus

Infrasound—affected structures and long-term exposure effects, ranked by sensitivity:

  1. Outer hair cells — “Overworked, tired, irritated” OHC, type II fiber stimulation
  2. Inner ear fluid homeostasis — Volume disturbance, endolymphatic hydrops
  3. Saccular hair cells — Stimulation
  4. Other, non-ear, receptors — Stimulation
  5. Inner hair cells/hearing — None

Sensitivity and sensations remain to be quantified: ear pressure or fullness, discomfort, arousal from sleep; ear fullness, tinnitus, unsteadiness; unsteadiness; stress, anxiety.

“Wind Turbine Syndrome” — You cannot hear what causes the symptoms!

We need more research to define the sensitivity of these processes.

Sounds you cannot hear …

  • can affect you.
  • can disturb you.
  • can harm you.
  • can cause disease: auditory and balance disorders, effects of sleep deprivation are serious (hypertension, diabetes, mortality).

Conclusion and Recommendations

For years, people have been told that infrasound you cannot hear cannot affect you. This is completely wrong.

Because the inner ear does respond to infrasound at levels that are not heard, people living near wind turbines are being put at risk by infrasound effects on the body that no one presently understands.

Until a scientific understanding of this issue is established we should not be dismissing these effects, but need to be erring on the side of caution.

For industrial turbines a cautious approach could require :

  • setbacks of at least 2 kilometers (1.25 miles).
  • in-home monitoring of both A-weighted (audible) and G-weighted (infrasound) noise levels 24 hours/day for all dwellings within 2 miles.
  • health monitoring studies for those living within 2 miles (with consent).


We need to stop ignoring the infrasound component of wind turbine noise and find out why it bothers people!

Wind turbine noise is not comparable to the rustling of leaves.

Editor’s note:  Our appreciation to National Wind Watch for re-formatting Dr. Salt’s talk in a Web-friendly manner.

  1. Comment by carol littleton on 11/17/2010 at 9:49 am

    This is all a bit too technical for me to evaluate. Nevertheless it fits with my overall evaluation of this renewable energy source–the fact that developers are less than open with residents in furthering their plans and are essentially bribing innocent municipal councils to keep plans secret until leases are signed with willing (bribed) landowners–raises the possibility that something is being hidden.

    In other words, if those who are to be living amongst and nearby the turbines knew of the plan they would likely oppose it–fears of declining property values, fears of potential health effects if not a desire to have their familiar landscapes remain as they were. In a democracy, this is not what we expect, yet it is happening all over.

    I, therefore, as a long time environmentalist have come to beleive that the corporate model for wind turbine development must be nixed in favour of a community model which would control siting. It is outrageous the way the developers and investors have used a NIMBY accusation against those who have been negatively affected! Good to see some technical verification of what some [people] experience.

  2. Comment by Itasca Small on 08/30/2011 at 2:43 am

    Thank you for the article and for the comment. I am one who is suffering from a wind plant and its infrasound and/or vibrations. The effects are travelling approximately 10.5 to 11.5 miles in our topography and geological structure here in Central Navajo County, Arizona. If anyone wants to do any testing here, please, be my guest! I am also one of the people who actually perceives infrasonic waves when close enough to them. It is extremely uncomfortable and causes me to need to escape as quickly as possible. I did feel the waves when visiting the wind plant one time and one time only! If anyone wants to test me, please, be my guest for that too!

    I suppose we should not be surprised by the argumentum ad hominem attacks of the pro-wind advocates. It is standard procedure for many people these days – if you can’t attack the facts, then attack the person. Unfortunately, a large percentage of people have been so indoctrinated that they believe anything that sounds good to them with no concept of scientific method and logical argument. And, when they think they might be accused of NIMBY or wanting to destroy the planet, well, we see the disastrous results happening all around us! They are willing to destroy individuals, animals, and the environment if they can feel good about themselves.

  3. Comment by Hube (France) on 12/19/2011 at 3:55 pm

    Hi Itasca! and everybody ! What you write, Itasca, is very interesting for me because everything I’ve read so far on this (great) site seems to be about turbines close to homes or visible most of the time, but I’ve not read all the comments everywhere yet and I’m sure turbines strike even when hidden. “My” six turbines are 4.5 miles away from my house and I can’t see them. But, God, I CAN hear them! (I live in a mountainous area in France. The wind blows all the time up there on the mountains tops, but not around here, and the turbines rotate almost all the time, day and night). For 17 months now, I’ve been hearing, actually hearing, with my right ear only, sorts of very low frequency sounds, like “MMMMMMM…….MMMMMM…..MMMMMMMMM…etc.”, separated by seconds of pure silence, and that just drives me crazy. Those crazy M&Ms are no candies, they’re very loud, like the horn of a boat, and they last hours, it’s unbearable. No sleep, no rest for the mind, never. I also experience very loud Wooshings sometimes, thumps really, which are clearly the blades passing the mast. And, third kind of noise, a continuous “washing machine” noise (“whooshing machine” would be more appropriate) in the background. Even when that whooshing noise is weak, very weak, I KNOW when they turn, I know when they don’t. It’s in the air. All those noises enter my house in turns, never together, and there’s no way of stopping them. The “M&Ms” sounds are the most common (and the worst). I’m the only one in the area to hear those sounds which only occur when the turbines are turning (I can see them from near here). It’s Silence as before when they’re at a stop (rare). “Silence as before”: I know many of you “brothers in harm” — and sisters, perfectly know what that means. When I think “The Sounds of Silence” was my favorite song when I was young, ain’t life ironical sometimes? That’s great Art… (hello Paul).
    In a car, has anyone noticed?,windows up and engine off, that noise is perfectly audible at least 10 miles away, and from that far it’s hardly lower and still audible in houses, I’ve checked.
    Have you tested this phenomenon in a car? Those low frequency sounds are stronger in small closed places, I use the test-in-the-car thing to know how far that crazy sound expands all around the countryside. When proof is made not hearing does not mean no harm is done, EVERYBODY, EVERYWHERE, will be concerned. Then, maybe…
    The more I read on this site, the more I realize we ALL say the same things. We’re altogether worldwide and very often terribly on our own within our personal experience or in our neighborhoods, or rooms, driven crazy at nights, abruptly awaken or needing to sleep, with every cell of our bodies WANTING us to sleep, and with the mind that just can’t. Prevented from sleeping when sleepy, broken awake in our sleep when sleeping… And then, it’s a night up.
    No sleeping late in the week-end mornings either. No wonder staying up all the time makes you feel down… No balance in there, the turbines play with you.
    The sleeping problem reminds me of something a friend of mine told me recently. I was explaining him about my “life with turbines”. He then told me that Man, our remote primitive ancestors at the beginning of humanity, could sleep with a quiet mind only after domesticating dogs (well, wolves, then). Before that, they had to keep vigilant, watchful, even at night. So they would sleep “with one eye only”, as we say in French. Only when their dogs would watch the surroundings for them, and warn them through barking, they could sleep “on their two ears”, as again we say in French, changing eyes for ears, God knows why. Well, my conclusion was that those turbines are throwing us backwards over thousands of years of evolution, by preventing us from “sleeping on our two ears”, because with turbine noise, your mind CANNOT rest quietly. What Pandora’s box those sorcerer’s apprentices playing God with their turbines have opened?
    You’re right with this NIMBY accusation they throw at us, Itasca. They also use the fact very few people are affected in the same places. There’s cracks in the wall, though. That’s how the light comes in, as Leonard Cohen puts it (I like this guy).
    That’s why sites like this one are so valuable for me. You seem to be much ahead of us there in the States or in Australia than we are here in France, and I’m very happy to have found this site (thank you, Nina and Calvin!). It’s good to TELL and to be sure you’ll be understood, as I understand everything I read here
    So good luck with you, Itasca, and to everybody fighting turbine blades.
    Blades, hey? We know where they ‘ll go, eventually: right into the heart of the problem.

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