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‘Sensing but not Hearing’: Latest from Steven Cooper on Wind Turbine Nuisance (Part 2)

By Sherri Lange -- November 6, 2019

“The description of wind turbine noise needs a terminological shift. The language should be pulsations at an infrasound rate with modulation of the entire signal at an infrasound rate (as in sensation detected by the ear).” [Cooper, below]

Q:  You referred earlier [yesterday] to your second paper at the ICA  that is linked to the synthesis paper. Maybe my question on ILFN ties in with the paper on Amplitude Modulation that raises questions as to terminology?

Cooper: Yes. The second paper on amplitude modulation is very important. Because what people are calling AM (by reference to the dBA signal) is incorrect. An electrical engineer will tell you that AM is the modulation (variation in the amplitude) of a carrier frequency (being a high frequency) that is modulated at a lower rate. The dBA is not a single frequency.

Turbines exhibit a tone at discrete frequencies of between 25 and 32 Hz (dependent upon the turbine model). In the ones I have measured it relates to the speed of the shaft that drives the generator. The gearbox is subject to changes in loading as the rotors rotate that must be transferred to the generator. The change in loading occurs at the blade pass frequency (“bpf”) – which is in the infrasound region.

If you take the definition of AM, then for a wind turbine having a carrier frequency of say the gearbox output shaft (a low audible frequency) then that signal can have variations in time at the bpf. Different wind speeds and different blade angles will give different levels of variation in the amplitude of that frequency. The pulsations should be there all the time the blades are turning.

The loading on the gearbox will change as the rotor runs around and these pulses will get transferred through the gearbox. (Whether it is the blade passing the tower or the change in wind loading along the blade to create a specific point where there is equal pressure along the blade will still give pulses).

So the gearbox output shaft speed is the carrier frequency and the modulation is the blade pass frequency. A narrow band analysis of the frequencies around this gearbox output shaft speed will show sidebands spaced at multiples of the blade pass frequency. That is classic AM.

In the Cape Bridgewater study when the turbines are producing power there is a peak around 31.5 Hz. At Capital WF it is 25.5 Hz (different turbines).  FFT (Fast Fourier Transform) for both turbines show the gearbox output frequency with sidebands. That is AM as defined.

Q:  So you say that turbines do produce Amplitude Modulation (AM) but it is only related to a low frequency, but the modulation occurs at an infrasound rate?

Cooper: Correct.

Q: But isn’t this ILFN? (Infra and Low Frequency Noise)

Cooper: No, it is LF being modulated at an infrasound rate so it is not infrasound as a sound.

Q:  But the swish noise is not low frequency, is it?

Cooper: Correct.  And this leads to the next point. The modulation of the dBA value cannot be AM because it is a broad band noise. Hence this is the issue of terminology.

If you take the swish noise in the regions of 800Hz – 2kHz there are no discrete frequencies and therefore that noise cannot be AM. You can use 1/3 octave bands to see the modulation of the amplitude, modulated at the bpf. But not AM (Amplitude Modification) by definition.

The modulation of the amplitude for the remaining frequencies in the audible range of the acoustic signature (such as the swish or thump) is not AM. This modulation is defined by Zwicker and Fastl (Psychoacoustics: Facts and Models) as “fluctuation” because the modulation rate is less than 10 Hz. Zwicker and Fastl say people sense the modulation by the hearing mechanism, but may not hear it.

Q: You are saying that in Psychoacoustics: Facts and Models, Professors Zwicker and Fastl identified “fluctuation” as the modulation of a sound where the modulation occurs at an infrasound rate – but specifically below 10 Hz?

Cooper:  Yes. They show that the ear has a particular sensitivity to the rate of modulation around 4 Hz and that the modulation has an excellent correlation between speech and hearing system.

Q:  So acousticians have had knowledge of modulation for a while?  Does this modulation cause a greater degree of annoyance?

Cooper: Correct. Leventhal (in the UK) provided a report in 2004 (for DEFRA) that cited work by Bradley (in 1994) on modulation of low frequency broad band noise at an infrasound rate to significantly increase the annoyance of the broad band noise. But it seems to have been ignored. Leventhal has stated in his evidence in Australia (a long time ago) that in relation to annoyance of wind farms, it is not infrasound but modulation of low frequency.

Q: Doesn’t this tie in with Rand and Ambrose’s work at Falmouth, where the issue was the pressure pulsations occurring at an infrasound rate?

Cooper: Yes and this ties in with Prof Salt’s work on the inner ear.  My pulsation analysis concept came after Prof Salt’s work using pure tones. So can Prof Salt’s work show the mechanism where the ear can respond to the fluctuations – being modulation at an infrasound rate.

Q:  In the UK there has been a discussion on excessive AM giving rise to a greater level of disturbance, but it uses the dB(A) value which as discussed above is not really AM?

Cooper: Right. What they have used is the modulation of the dB(A) level at an infrasound rate.  It is simply incorrect terminology.  Being an electrical engineer first permits me to understand AM and filter theory.

Q:  Your AM paper discusses a modification of one format for deriving AM used in the UK and the Modulation Index.

Cooper: Yes. A number of years ago we developed a method to show the variation in the wind turbine signal over time that showed the pulsations, amplitude modulation and frequency modulation. It helped acousticians understand the time varying nature of the signal. In the synthesis paper there is a link back to our website that has examples of narrow band and 1/3 octave band “movies”.

The UK method is time consuming in determining the modulation index.

We used the underlying analysis concept for our “movies” to determine the statistical analysis in 1/3 octaves for multiple 10 minute samples of wind turbine noise and derive the modulation index of the A-weighted peaks in the spectrum by taking the L1 level minus the L90 level (to agree with parameters used in Australia). The results agree with the labour-intensive method of manually determining the Modulation Index using multiple sets of 10 second samples.

I presented the Modulation Index information for the various wind turbine noise samples (and non-wind turbine samples) in the brainwave paper. The third paper on the brainwave monitoring is just a pilot study but identified the impact on the frontal lobes.

Q:  Yes: the third paper is different, and whilst only a single person test pilot study it would seem to show the automatic response of the brain to the presence of inaudible sound.

Cooper:  Yes. The paper can only discuss the acoustic content of the testing. It was the next step from the work presented in ASA (American Society of Acoustics) in New Orleans and Euronoise and the brain wave results presented to the audience are not in the power point for public viewing as they are the results from the psychologist who undertook the measurement and analysis.

Q: Well, there is a lot to digest in your three papers given at the ICA (International Congress on Acoustics) and I see that we have to consider a change in terminology as more is learned about wind turbine noise.  I see that your work is practical field work using real wind turbine noise and you are still undertaking this work with no funding.  Could you summarise the key technical points from your latest work?

Cooper:  There are other researchers working at the ‘coal face’ in getting to the bottom of the wind turbine noise issue and their work is important and blends in with my investigations.

I suggest that with respect to the description of wind turbine noise it is a matter of terminology that needs a shift as follows:

  • The language should be pulsations at an infrasound rate.
  • Modulation of the entire signal at an infrasound rate. (Zwicker and Fastl call this fluctuation as a sensation detected by the ear).
  • AM is present as some discrete low frequencies modulated at the bpf.
  • UK method of AM is determining the modulation index of the fluctuating signal (not technically AM).
  • You can determine the Modulation Index of the low frequency noise that is AM.

As a result of work I conducted in 2013 as to detected by residents of the operation of the turbines when the FFT (Fast Fourier Transform) levels in the region of 4 – 6 Hz were above 50 dB that led to the re-discovery of Kelley’s work of the 1980’s, one can  expand Zwicker and Fastl’s work, and Bradley’s work, to determine the annoyance adjustment for wind turbine noise. That is one of the next projects I am looking at.

Conclusion (Lang)

We sincerely thank Mr. Steven Cooper for again explaining not only his technical work, but also for his diligence in pursuing the in-depth nature of the complexities of the peculiarities of wind turbine “noise,” and relating those to actual real time experiences of people living near wind turbine factories.

Above all, noted is the volunteerism of Mr. Cooper’s ongoing research. We emphasize that Mr. Cooper’s re-definitions and research augment the measurement of  ILFN (Infra and Low Frequency Noise) and do not in any manner diminish the validity of the general discussion in relation to impacts. The shift in identifying the correct terminology and definition of amplitude modulation and fluctuation complements the work of other notable acousticians and researchers (as did Cooper’s identification of sensation and his double-blind studies on inaudible wind turbine noise).

The impacts are repeatedly proven to seriously impact persons, and animals. Cooper’s recent articles reinforce the ground breaking work of Zwicker and Fastl (that has been forgotten/ignored by the wind industry) and that of Kelley (that has also been ignored by the wind industry until Rand, Ambrose, James and Cooper “rediscovered” the Kelley work in 2014).


  1. Sherri Lange  

    I would like to share a document that came today, referencing this Cooper Interview, and Google translated from Finnish, although it references materials from Germany. Thank you again, Steven Cooper, for your generous time sharing your newest research with us, and for also your incredible volunteerism. It is noted around the world.



    Posted by: Doctors and Scientists from Germany.
    April 2019

    Open letter to political leaders on:
    Technically produced infrared sound

    Ladies and gentlemen, we, the senders of this letter, have been working on this subject for a long time and our concerns are growing:

    The infrasound sound emitted by technical devices such as wind turbines is underestimated as well
    • their severity that
    • the epidemiological significance

    Current standards for the protection of the population do not correspond to the latest scientific findings. We explicitly emphasize that these effects far exceed normal levels of harassment.

    These are diseases:

    • Serious illnesses and their symptoms range from major sleep disorders with organic effects to secondary diseases, to physiological hearing loss and other disorders, to myocardial cell loss and to increased anxiety disorders.
    The symptoms are manifold. One symptom affects several physical and psychological functions. Many of these effects have not been studied or understood at all

    The estimated number of sufferers is bleak, especially since not all physicians are aware of the causal relationship of illness to the technical infra. The distance rule is therefore only the tip of the iceberg. Estimates of the total number of victims in the Federal Republic range from thousands to hundreds of thousands.

    The resulting health costs of early disability and job loss are hardly measurable.
    Scientific studies and opinions generally end with “Other studies are necessary”. This statement is misinterpreted by government and government parties, meaning that there are no health effects. These statements are also used in decision-making by the courts.

    The construction of German wind power will continue, with inevitably dramatic effects. Given the infectious diseases already revealed and their epidemiological scope, we believe that the precautionary principle requires urgent action by the political leadership. The safety of wind turbines and the grounds for their regulation must be redefined.


    Dr. Eckhard Kuck from the Doctors’ Forum Immission Control Bad Orb,
    Prof. Dr. med. Med. Johannes Mayer
    Professor Dr. med. rer. nat. Werner Roos (pharmaceutical biologist),
    Dr. med. Dagmar
    Schmucker (internist)
    Prof. Dr. med. Werner Mathys (formerly Lei-ter)
    Environmental Hygiene and Environmental Medicine, University of Münster), Prof. Dr. med. Lothar W. Meyer
    Dr. med. Med. Walter Tutsch, dr. Med. Dorothea Fuckert {FA for
    General Medicine, Waldbrunn)
    Dr. med. Med. Manfred Fuckert (General Medicine FA,
    Dr. med. Bernhard Voigt (Occupational Health Care FA, Gaggenau), Dr.Med. Martina Ohlmer (Moringen)
    Dr. med. Kuno Veit (general practitioner, Dittmarschen),
    Dr. med. Almut Finke-Hain (Obstetrics and Gynecology)
    Dr. med. Med. Herbert
    Klengel (FA Radiological Diagnostics)
    Dr.med. Ulrike Borrmann (General Medicine FA,
    Esens Ostfriesland)
    Dipl. psych. Gisela Antony (Marburg)
    Dr. med. Jürgen Strein (FA General / Occupational Medicine)
    Dr. med. Heinz-Jürgen Friesen (Marburg)
    Dr.med. Heinz Kellinghaus (Department of Internal Medicine / Naturopathic Medicine, Münster)
    Prof. Dr. Med. Jürgen, Rochlitz, Burgwald
    Dr. Med.Bernhard Kuny (FA, General Medicine / Naturopathic / Chirotherapy Glottertal)
    Dr. med. Anita Schmidt-Jochheim
    (Physiology and Obstetrics)
    Dr. Med. Susanne Kirchhof
    Dr. med. Regina Pankrath
    (General Medicine FA, Zos-sen)
    Dr. med. Med. Klaus Pankrath (pediatric surgeon)
    Prof. Dr. med. Thomas J. Feuerstein, (Doctor of Neurology and Psychiatry, Doctor of Pharmacology and Ph.D.
    Dr. med. Habil. Eberhard Franz (dermatologist-allergist)
    Prof. Dr. med. Stoll
    Dr. med. Karsten König (Cardiologist, Internal Medicine FA, Damme) ”

    Addendum: Professor Christian-Friedrich Vahl, Director of Cardiac, Thoracic and Vascular Surgery at Johannes Gutenberg University, in a German documentary in the summer of 2019, estimates that several million Germans suffer from severe sleep disorders, heart disease, nausea, lack of ability to concentrate. https://www.zdf.de/dokumentat…/planet-e/infrasound-100.html…

    Should infrared heart rate be reached throughout the country so that sufferers will never have the opportunity to move to a pulsed zone? Why do representatives continue to continue the German disaster? You must have a good reason for this. “


  2. Weekly Abstract of Local weather and Power # 385 – Next Gadget  

    […] ‘Sensing but not Hearing’: Latest from Steven Cooper on Wind Turbine Nuisance (Part 2) […]


  3. BoyfromTottenham  

    Mr Cooper repeatedly refers to traditional sound level meter readings with ‘A weightings’. My understanding, from using and studying the technical specifications of traditional sound level meters (such as B&K models) is that, despite being required under many environmental protection agencies’ wind turbine noise measurement legislation, are technically incapable of accurately measuring frequencies below about 20 Hz, and if an A weighting is applied, will attenuate any input in this range by a large factor, as determined by the A weighting scale developed many decades ago from the response of the human ear. One might well ask why legislation purporting to ‘protect the environment’ would mandate the measurement of wind turbine by an instrument that is technically incapable of measuring frequencies below 20 Hz, the very frequencies that are the subject of so much argument about the adverse health effects of these turbines.


  4. steven cooper  

    I agree with you comments about dBA measurments.
    The environmental authorities have nominated dBA for wind turbine noise measurements and have based the assessment criteria of road traffic noise also measured in dBA. The sound of road traffic noise is not the same as wind turbine noise AND the are no dose-response curves to identifiy the level of wind turbine noise that will not cause sleep disturbance.
    The general concept of Amplitude Moulation based on the dBA level is incorrect (see second ICA paper). My Capebrigewater Study showed the dBA level was correlated to wind speed and not the output of the wind farm.
    I have questioned for years the presence of sounds below 10 Hz. The signal shows in the time domain pulsations at an infrasound rate – but that is not a sound in the infrasound region.
    The interview referred to using correct terminology.
    The problem that exists with the incorrect use of Amplitude Modulation is that many people assess the modulation of the dB(A) level. I used the same methodology to compare my simplified assessment procedure, but in the Amplitude Modulation paper and the brainwave paper I presented the Modulation Index in both Linear and A-weighted results for determination of the Modulation Index to describe the noise. Adverse health effects are outside my scope of expertise.
    By the way, I use B & K instrumentation with much higher sample rates than general sound level meters to overcome limitations of normal sound level meters – which is an entirely different area of discussion but extremely important when using wind turbine noise as the source for subjective assesssment – that MUST be recorded as Linear (un-weighted) results.


  5. Sherri Lange  

    Today was reminded in an email from Europe of the plight of Master Gardener, Boye Jensen.


    “Boye Jensen’s big problem is that the authorities are still not sure that giant wind turbines make people sick, and it is uncertain whether he can get compensation. But the 67-year-old nursery owner is going for a compensation in the millions. “I am closing my business because of the turbines. Otherwise I would have continued for 6-7 years, and then I would have put the nursery on the market. But now the property is unsalable.” (More personal tragedy for the Jensen family ensued.)

    “First, together with my lawyer, we need to find out whom we will take to court: Vattenfall, which own the turbines, or the municipality of Holbæk, which approved their installation.”


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