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« Men of no meaning | Main | Skary kidz extreme weather - Josh 250 »
Friday
Dec062013

Windfarm noise: state of play

Via Angela Kelly comes this message from acoustician Mike Stigwood, who sets out the state of play on excess AM noise from windfarms. It looks like surrender from the developers.

Recent research presented at three planning inquiries that were conducted in September, October and November (Starbold, Bryn Lleweln and Shipdham - decisions awaited)  have hopefully exposed the misconceived arguments made by the industry's acousticians, which have successfully avoided controls over wind farm noise impact for many years.

After more than 4 years of smoke screens, obfuscation and erroneous objections raising unrealistic concerns and placing barriers in the way of necessary controls over the wind farm noise called "Excess Amplitude Modulation", industry acousticians have finally admitted a planning condition is "necessary" and "reasonable".  Excess AM is now shown to be neither rare nor only causing minor effects as claimed over the last few years, arguments that have successfully blocked planning controls leaving many communities exposed to serious noise impact.  Research by ourselves and the Japanese have exposed this as a common and serious problem.

Dr Matthew Cand of Hoare Lea is part of the Renewables UK research team on EAM who were due to report their findings over 2 years ago but have continuously deferred this.  He finally admitted after 2 hours of cross-examination, when being questioned over the need for a condition at the Shipdham Inquiry last week, that one was both necessary and reasonable.  Dr Cand was also questioned over the Den Brook condition metric which was accepted in 2009 but rejected ever since and that was formulated by MAS Environmental with a 3dB(A) EAM limit.  This has been subject to widespread industry attacks over the last four years, leading to its rejection by planning inspectors ever since the Den Brook decision.  In response Dr Cand said "If I had to pick a number I don't think 3dB(A) is a bad number".  In effect the Renewables UK research must support what we found four years ago.  

These admissions follow years of unpublished work by Renewables UK, coupled with statements that no one knows the appropriate level.   In September at the Starbold Inquiry arguments that the Den Brook condition was triggered by extraneous noise were dropped by the appellants and they accepted it was an incorrect argument.  Following the Bryn Llewelyn appeal in October 2013 Dr Jeremy Bass of RES, the main opponent of the Den Brook condition said during a meeting "foolishly ... we went along the industry line that amplitude modulation is rare". He accepted the argument that it can be dealt with by statutory nuisance was wrong.  He continued:

I think that argument is completely exploded by the weight of evidence presented by Mike Stigwood in particular .... we are in a difficult position now ... the landscape has changed and I suspect .... in the future developers will no longer try the argument that AM is rare.

It is hoped decision makers will no longer receive erroneous arguments about the control of EAM and that conditions following the Den Brook metric are now applied to all future consents.  There also needs to be a mechanism developed by Government for applying it to existing wind farms.  Emerging evidence from the Japanese studies suggests a stricter limit may arguably be necessary but at the present time it is safe to consider the Den Brook metric as a means of controlling wind farm noise.

We also hope decision makers will now exercise particular caution with respect to arguments made by wind industry acousticians and that those who raise concerns over wind farm noise, in the main, do so legitimately.

If anyone seeks further information on appropriate forms of control of this common noise problem they can visit our website at www.masenv.co.uk for more information or email us direct.  
    

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Reader Comments (38)

Big Wind reminds me of Big Tobacco with all the years of denial.

Dec 6, 2013 at 3:46 PM | Unregistered CommenterConfusedPhoton

This is a separate issue to whether wind turbines are useful additions to the grid. (They are not and never will be in my opinion)

Wind turbine noise might or might not be a real issue in some or all cases, backed up by solid studies, but some of the campaigning reminds me of anti-fracking hysteria or going back further, mobile phone mast panics.

Still, it's nice to see the boot on the other foot for a change. They are doing all the dodging and prevaricating that they accuse Big Oil of.

Dec 6, 2013 at 4:02 PM | Unregistered Commenterkellydown

I watched my sister going to pieces because of noise from a nearby wind farm. She lived on an organic farm and was in favour of wind turbines until low frequency noise made her very ill. In the end she and her husband had to sell their beloved farm. Anyone who doubts that there is a problem hasn't seen the effect of turbine noise on someone who is perfectly normal and healthy. I thought that it was going kill her.

There is the question of why it affects some people but not others. When she had her hearing tested it was found to be unusually sharp. 'You have the ears of a bat' might be good news, but not if there is a wind farm up the hill.

Dec 6, 2013 at 4:26 PM | Unregistered Commentermariwarcwm

One brick at a time.
That must be getting for a whole wall by now!

Dec 6, 2013 at 4:50 PM | Registered CommenterMike Jackson

Expensive, unavailable at periods of high demand, destructive of wildlife, despoiler of landscape and harmful to human health.

What's not to like?

Dec 6, 2013 at 5:04 PM | Unregistered Commenterssat

The inaudible low frequency noise that causes wind turbine syndrome (see Nina Pierpont's book of the same name) is a separate issue from EAM. EAM is heard as a thumping or swishing sound that occurs at blade passing frequency. It occurs mainly in the evening and at night, particularly in conditions of high wind shear. It wakes people up, drives them to distraction and stops them getting back to sleep. The lack of sleep results in ill-health.

I too have tried to get local environmental health officers and Planning Inspectors to take the problem seriously, but none of them will. They fall back on the argument that it hasn't been proven and that the Government does not recognise that such noise is a problem and can cause ill-health. Of course the Government has funded the wind industry to do research into the problem and takes guidance from the wind industry. There are many in the wind industry who should be in prison because of their actions in denying the problem and covering up the truth for years. Hundreds of people have had, and continue to have, their lives made a misery and their health seriously damaged.

Mike Hulme of Den Brook and Mike Stigwood are hated by the wind industry, but are real heros of us anti-wind campaigners.

Dr Jeremy Bass of RES was the acoustician of RES battling with Mike Hulme for years over the Den Brook EAM noise condition. I've seen Bass in action against Mike Hulme - his confession is long overdue.

Dec 6, 2013 at 5:10 PM | Registered CommenterPhillip Bratby

Next question: What are the longer term ramifications for operating wind-farms after considering possible legal actions from those claiming for health-related injury?

Dec 6, 2013 at 5:25 PM | Unregistered Commentermichael hart

If dB(A) here has its usual meaning, it seems a very odd choice to me as a scale for measuring infrasonic energy levels. It has a pronounced peak in the upper midrange, and rolls off sharply above and below this, being intended originally as a measure of machine noise in factory environments. IIRC, by the time the curve reaches the single-figure Hertz range of windfarm noise it's about 50dB below its midrange value, a huge attenuation.

If I were measuring infrasonic energy, I'd want a meter with a decent infrasonic response, not one using a scale which reduces the frequency range of interest by such a large factor. Even dB(C) (used for assessing music levels) would be far better pro tem, although the fact of windfarm noise really calls for a standardised curve to be developed which would be capable of isolating (say) the sub-10Hz range from everything else.

Dec 6, 2013 at 5:25 PM | Unregistered CommenterSteve C

Some really good news, for a change. We'll watch with interest the efforts of Dopey D. and the troughers to circumvent the empirical data.
I agree with Philip Bratby. I get more and more angry with the politicians, environmentalists and so called scientists involved in promoting CAGW and renewables.
In times gone by, the French would have been oiling the tumbril wheels and sharpening the knitting needles.

Dec 6, 2013 at 5:41 PM | Unregistered CommenterG. Watkins

Big Wind. Deniers of sleep deprivation caused by AM. Deniers of cheap and reliable energy provided by fossil fuel, and the fuel poverty created by their subsidy farming. Deniers of their massive negative environmental impact that their dominating structures are having all over Britain.

They trash our Nation, our lives, and reduce us to poverty in pursuit of their hypocritical greed. The three D-greeds.

Dec 6, 2013 at 6:43 PM | Unregistered Commenterfenbeagleblog

mariwarcwm

I am very sorry to hear of your Sister's plight. Very similar problems have been experienced and well documented in both USA and Australia although neither authority will accept it even though the evidence is compelling.

Dec 6, 2013 at 6:48 PM | Unregistered CommenterRoss Lea

Good work by Mike Stigwood to expose the Big wind lies.

However I suspect is will be a moot point now that the Government is cutting support for onshore windmills
and increasing subsidies for the offshore follies.

Dec 6, 2013 at 7:23 PM | Unregistered CommenterDon Keiller

Anyone else hearing the cogs in Fenbeagle's mind turning?

Dec 6, 2013 at 7:41 PM | Unregistered CommenterAdam Gallon

Mike Stigwood's presentation last week to the Scotland Against Spin conference can be found here. Read it and see how residents of the countryside have been sacrificed so that big wind can screw the citizens.

Dec 6, 2013 at 7:52 PM | Unregistered CommenterPhillip Bratby

The British are happy payers for the nuclear cost, and the 80 billions to deal with nuclear waste.

If WTS would exist, people living near shores would be very unhealthy.
But people living near shores where they constantly hear the waves pounding on the beach, or the rock, are very healthy.
When that noise does not make them sick, then also the noise from wind turbines is harmless.

In the Netherlands, hundreds of farmer families live within 100 meter from a large turbine near the farm house, and they remain healthy for years. They falsify the relation between WTS and wind turbines, or the relation between sound from turbines and sickness.

This is just a new form of fossil promotion sickness, people are paid to extend the live of polluting power plants

The anti wind activists and their propaganda are mechanisms that make people sick

Dec 6, 2013 at 9:20 PM | Unregistered CommenterHenk Daalder Wind Farm Wiki

When the True Believers next bring up the lies and hidden research concealing the dangers of smoking, maybe this would be an appropriate response. It is not the sceptics who behave like the smoking industry did in hiding the dangers inherent in their product, it is the wind energy industry. The difference is that the evidence showed smokers were harming themselves, the wind industry harms people who have no say in the matter.

Dec 6, 2013 at 10:31 PM | Unregistered CommenterDoubting Rich

In the Netherlands, hundreds of farmer families live within 100 meter from a large turbine near the farm house, and they remain healthy for years. They falsify the relation between WTS and wind turbines, or the relation between sound from turbines and sickness.

Are you aware of the argument that used to go" My father smoked every day of his life and he lived to eighty, so obviously smoking isn't bad for you. It was a crap argument then, just as yours is today.

I'm fairly sceptical of the illnesses posed by wind farm noise, although slightly more likely to suspect the low frequency issues (at least partly because low frequency vibrations make me very unwell in planes and buses, even though people beside me don't seem to notice). There is a whiff of the "cell phone towers give me migraines" we had a few decades back. However your "arguments" that it must be all in their minds, on the basis that you don't like the anti-wind activists, is not helpful.

The British are happy payers for the nuclear cost, and the 80 billions to deal with nuclear waste.

Of course they are happy. The nuclear plants provide extremely reliable sources of energy.

Dec 6, 2013 at 10:31 PM | Unregistered CommenterMooloo

Henk Daalder, another denier of scientific evidence, a trait common to those in the pay of big wind, where human health counts for nothing.

Dec 6, 2013 at 10:35 PM | Registered CommenterPhillip Bratby

I'd still prefer the take matters into my own hands method. Estes rockets trailing a length of nylon cord ought to do the trick.

Dec 6, 2013 at 10:50 PM | Unregistered Commenterpapertiger

WHAT WAS THAT???

Dec 6, 2013 at 10:55 PM | Unregistered Commenterjones

What is "Excess Amplitude Modulation" please?

Dec 6, 2013 at 11:14 PM | Registered CommenterMartin A

The first documented reports of people complaining about low frequency wind farm noise date back to 1979. These complaints triggered extensive testing from 1981/82 onwards on low frequency noise emitted by wind farms - how it annoys people, how buildings amplify the noise certain frequencies, how people's health can be affected.

One paper published in 1985 recorded infrasound (noise below 20 Hz frequency) over 10 km from the source (a single wind turbine).

Dr Neil Kelley proved under laboratory conditions that the low frequency/ infrasound component of noise can make people ill, and that increased exposure to low frequency noise & infrasound is cumulative, making people's health worse over time.

Kelley presented his paper to the Windpower '87 conference in Los Angeles in Oct 1987. Kelley's paper also recomending measures which should be adopted by the windustry to minimise exposure of people to low frequency noise.

The windustry has known about the the adverse effects of low frequency noise on health since at least 1987. Not surprisingly, the windustry has ignored the recommendations published by Kelley. In fact it continues to reject Kelley thorough research. The windustry has consistently rejected ALL research casting a negative light on the subsidy generating industry.

I had a letter from Gregory barker MP earlier this year when my MP forwarded a letter I sent him highlighting my concerns on the effects of low frequency noise on health. The govt's view is that wind farms to not have an adverse effect on people's health.

One of the documents which supports the govt's position is a literature review on low frequency noise commissioned by DEFRA in 2003. This review was conducted by Dr Geoff Leventhall. Leventhall knew of the research carried out in the 80's & 90's (he mentioned the research twice in passing his report). However, he did not review any of the documents to reach his conclusion that wind farms do not emint enough infrasound & low frequeny noise to harm people's health. Not one of the research papers I refer to above were in Leventhall's list of references.

ETSU guidelines only stipulate measuring noise with an A-weighed filter applied. This filter is desigend to measure only the noise normally heard in human speech. It has the effect of significantly de-emphasising low frequency noise, and virtually ignoring all infrasound. These A-weighted readings are just a con - they don't measure the whole noise spectrum. By complying with ETSU-R-97 guidelines, wind farm operators are able satisfy the noise requirements most of the time.

All this evidence points to a scandalous cover up by BIG WIND & by the govt on the adverse effects of infrasound & low frequency noise on people's health.

My wife and I live in a very quiet rural location. We can both hear LFN (low frequency noise now). My wife is very sensitive to it. She can hear it from at least 25-30 miles away when the atmosphere is particularly stable. I have plenty of observations to back my hypothesis, including a noise recording (10 Hz to 20,000 Hz frequency spectrum) but no scientific proof yet. The loudest noise recorded in our home was in the infrasound to low frequency spectrum (10 - 100 Hz).

Dec 7, 2013 at 12:32 AM | Unregistered CommenterE Griffiths

@ Dec 6, 2013 at 10:50 PM | papertiger

Skip the Estes, go to an Aerotech K250PW High Power engine, 2,500 N-sec of thrust. Drop the nylon (much too stretchy)and sub in 1/16" or 3/64" stainless steel aircraft cable. Ignite and enjoy!

Dec 7, 2013 at 1:47 AM | Unregistered CommenterD. J. Hawkins

Off topic but Michael Mann up to his usual here:

http://www.businessinsider.com/scientist-rips-apart-the-new-york-times-coverage-of-climate-change-2013-12?pundits_only=0&comments_page=0#comment-52a28c096da811ac1fa704d5

Dec 7, 2013 at 3:12 AM | Unregistered CommenterRB

Some friends in the horsey set say they can't have turbines near the stables because it drives the horses nutty. Thats annectdotal..........anyone have any info on the effect on animals with better hearing than us? I tried asking a horse but he said nay. (sorry..).

Dec 7, 2013 at 3:13 AM | Unregistered Commentermikef2

Martin A asks What is "Excess Amplitude Modulation" please?

E Griffiths has given an excellent explanation of infrasound, but Excess Amplitude Modulation (EAM) is a totally different phenomenon. EAM is just Amplitude Modulation (AM) with an increased magnitude of the modulated noise. AM is noise of varying amplitude that occurs at blade passing frequency. Thus a 3-blade turbine rotating at 20rpm emits AM once per second as a blade passes the tower. The wind industry claims not to know the cause of the noise, but it is generally considered to be a combination of effects involving blade twisting and turbulent air from the blade's trailing edge and tip hitting the tower.

As E Griffiths has said, noise is controlled by the limits given in ETSU-R-97. The limits include 3dB max-to-min for AM. 3dB is used because a change in noise of that magnitude is not very discernible. But ETSU-R-97 gives a noise limit as a function of wind speed, measured at 10m height (or extrapolated from measurement made at, for example hub height - another controversial issue due to wind shear) averaged over 10minutes. So if AM is greater than 3dB max-to-min, it is averaged and is not controlled by the ETSU-R-97. If somebody experiences EAM from a nearby turbine, there is nothing they can do about it. If the person complains, the wind turbine owner will be told by the local authority environmental health department to monitor the noise. He will do that, but his measurements of the EAM will disappear in the averaging process and he will show that the turbine noise continues to meet the ETSU-R-97 absolute noise limit averaged over 10minutes.

EAM can occur with peak-to-min of much more than 3dB. Mike Stigwood has measured well over 10dB. It can be clearly heard as a regular thumping or banging noise. Mike Stigwood claims all industrial wind turbines emit EAM.

Mike Stigwood has measured EAM at many wind farms and individual turbines. It is a very complex issue, highly dependent on atmospheric conditions, wind speed, wind dirtection, layout of turbines (for a wind farm), distance from turbines etc etc. The worst occurrences are in the evening and at night when high wind shear occurs due to stable atmospheric condition (the wind speed is high at hub height but low near the ground) and there is little background noise to mask the EAM. The effect can be worst at hot spots which can be indoors. The EAM can occur in short bursts which repeat at irregular intervals or can go on for long periods. The health issue arises because people are woken repeatedly (if they can get back to sleep between times) or cannot get back to sleep because they are anticipating the next burst of noise). Ill-health arises because of the lack of sleep or the disturbed sleep (see the work of Dr Chris Hanning, the country's leading expert on sleep disorders, for more info). Health disorders due to EAM are completely different from those due to infrasound described by E Griffiths (see Dr Nina Pierpont's book on Wind Turbine Syndrome)

Successive Governments (well the civil servants) and the wind industry have conspired together and have denied the issue of EAM for years and have covered it up for years, despite world-wide evidence to the contrary. This is just the same as they have denied infrasound as E Griffiths has explained earlier. More and more evidence is coming from around the world that EAM is real and causes huge health issues for residents near to wind turbines.

Dec 7, 2013 at 7:24 AM | Registered CommenterPhillip Bratby

EH?

Dec 7, 2013 at 7:25 AM | Unregistered Commenterjones

Simple solution : no turbine allowed within 10 Miles of a dwelling ?
Existing ones given 12 months to comply.

Dec 7, 2013 at 7:43 AM | Unregistered CommenterTomcat

Dec 7, 2013 at 7:24 AM | Registered CommenterPhillip Bratby

Philip - thank you.

I'm still not completely clear. I can understand (I've heard it myself) that noise from a wind turbine is random noise but with periodically varying amplitude. [In the distant past I've heard of similar signals being termed 'cyclostationary' - their statistics vary periodically with time.]

I'm not clear what constitutes "excess" amplitude modulation. Some difference between max and min signal that exceeds some threshold, perhaps? Is there a technical reference that defines the term precisely? Given a recording calibrated for amplitude, how would I compute the excess amplitude modulation of the signal? What units is it measured in?

Thanks again.

----
Re-reading your informative comment, I think that excess amplitude modulation is amplitude modulated noise where the max (in dB) - min(in dB) > 3dB. ie the maximum amplitude is more than 1.4 times the minimum amplitude.

But I'm still not clear what units (if any) it is measured in.

Dec 7, 2013 at 9:11 AM | Registered CommenterMartin A

But what does this mean. That all NEW turbines have to comply ?

Dec 7, 2013 at 9:27 AM | Unregistered CommenterAgrestis

Martin. I don't think there is an agreed definition of EAM. In 'Wind Turbine Noise Impact Assessment Where ETSU is Silent. by: Richard Cox, David Unwin and Trevor Sherman', they say the following:

What is amplitude modulation?
Amplitude modulation is the cyclic variation of sound energy emitted by a wind turbine. These cyclic variations occur at the blade passing frequency (about once per second) and normally give rise to the characteristic ‘swish’ noise. For much of the time this characteristic noise can be relatively benign but under certain conditions the nature of the noise changes to what is often referred to as excess amplitude modulation (EAM). EAM is generally recognised as being when the swish of the turbine blades changes to a more pronounced thumping or banging noise. EAM is highly intrusive and can be experienced at receptor locations over 1.5km from turbines. It should be considered as being additional to the normal turbine noise and its occurrence at any particular site cannot at present be predicted with a high degree of certainty although it tends to be associated with high wind shear conditions and large wind turbines.

It is measured in dB(A), ie weighted to the human ear - which is why infrasound is ignored at it is, by definition, at a frequency below that which humans can hear.

It is a complex issue and you need to read the above paper and work by Mike Stigwood to get a good handle on it.

Dec 7, 2013 at 9:46 AM | Registered CommenterPhillip Bratby

Despite the warmist language, Henk Daalder's post does contain a valid point.
It seem that this form of noise does not affect everyone, or not to the same extent. A pure guess is that a few are strongly affected, some are mildly discomfitted and some are impervious.
It looks like a strong argument for much greater separation distances when proposed sites are near habitation but that will not help campaigns against windfarms on open moors and such.

By the way Henk, the £80bn tag is for clearing up Sellafield (primarily) and addresses the residue from the weapons programmes of the postwar and coldwar decades. It is not relevant to modern nuclear power.

Dec 7, 2013 at 11:29 AM | Registered Commentermikeh

mikeh:

Henk Daalder was talking nonsense. WTS is caused by infrasound, which we cannot hear, and so has nothing to do with the noise waves make when pounding on the beach. He doesn't say what the size of the turbines are that people live within 100 meters [sic] of, but anybody willingly living within 100m of a modern industrial wind turbine would need sectioning.

Dec 7, 2013 at 11:42 AM | Registered CommenterPhillip Bratby

All good stuff - what news of Pat Swords and the ratification of the Aarhus Convention on Human Rights..?

Dec 7, 2013 at 12:45 PM | Unregistered CommenterSherlock1

Henk

"hundreds of farmer families live within 100 meter from a large turbine near the farm house, and they remain healthy for years"

They're not likely to complain if it removes their subsidy...

Dec 7, 2013 at 1:42 PM | Unregistered CommenterJames P

Thanks Phillip.

I confess I was assuming that EAM causes - or contributes to - Wind Turbine Syndrome until I went back and read your 5:10 post of yesterday more carefully. Maybe Henk D did the same with his point about surf noise.

This makes me realise that I have only ever seen these things at a fair distance so, when opportunity presents, I will make a point of getting close to one (living in Surrey, the nearest is probably the one at the Majedski stadium in Reading but I believe that is a relative tiddler).

Dec 7, 2013 at 2:45 PM | Registered Commentermikeh

Philip Bratby, I'm not an acoustician. My understanding is that amplitude modulation is the pulsating of the sound (continually variable volume in layman's speak) emitted by wind turbines. I believe this to be caused by the interference patterns created by pressure waves generated by each turbine in a cluster. Sometimes you get 2 or more pressure pulses combining, increasing the intensity of the sound. Similarly you can get 2 or more pulses of rarefaction (low pressure) combining. yet at other times you can get a pressure pulse & a rarefaction pulse interacting, cancelling each other out. Someone please correct me if I'm wrong.

When you get 2 or more wind turbines in a cluster, the interference patterns can be incredibly complex since the turbines are likely to be slightly out of phase relative to each other.

I was observing 2 wind turbines, one behind the other yesterday, and noticed they rotated at slightly different speeds. That again would add to the complexity of predicting amplitude modulation.

Some people CAN hear infrasound - ILFN - (certainly at the higher end of the infrasound scale - >0 - 20 Hz), my wife being one. She started hearing infrasound in 2006, after a wind farm was commissioned 25 miles from our home. After several years of observations, I believe the 2 to be related. We've even had the infrasound measured in our home (down to 10 Hz anyways due to instrument limitations) to prove that the noise is not a figment of my wife's imagination.

Since the inital observations other wind farms have popped up closer to our home. Last summer my wife became ill for about a month, with classic symptoms associated with "wind turbine syndrome". The symptoms started several days into a period of constant loud LFN/ILFN. Initially, when we went out for the day my wife would start feel better after several hours away from the noise. As her ILFN exposure time increased going out for several hours did not alleviate her symptoms.

It was only after the weather broke and the ILFN greatly diminished (or disappeared) that my wife started recovering again. It took 10-14 days to make a full recovery. Her doctor diagnosed labyrinthitis (inflammation of the inner ear) which can induce some of the symptoms of wind turbine symptoms - ie. motion sickness and loss of balance. However, after piecing all the bits of information together, we believe she suffered from exposure to ILFN. By the way, the nearest wind to us is 8.5 miles away and is hidden from view by a 300m high hill.

Dec 7, 2013 at 3:57 PM | Unregistered CommenterE Griffiths

"The wind industry claims not to know the cause of the noise, but it is generally considered to be a combination of effects involving blade twisting and turbulent air from the blade's trailing edge and tip hitting the tower"

Then the wind industry knows nothing about aerodynamics - as a flying enthusiast I am well aware of the noise caused by close proximity of propellers to any fixed part of an aircraft. The Cessna 336/337 and Military derivatives have one of two engines mounted at the rear, and a twin boom arrangement to support the tail. This leads to shock waves being reflected from the booms as each prop tip passes. The distinctive rasping noise is very evident at about 20 seconds from the start in this YouTube clip:

http://www.youtube.com/watch?v=HV5n0FjAQ1I

Obviously the amplitude and frequency are very different than with a wind turbine, but exactly the same effect can occur when each blade tip passes close to the ground, in addition to turbulent airflow hitting the hollow tower. Since this is anchored to several hundred tons of concrete buried in the ground, I can't think of a better sounding board...

Dec 7, 2013 at 4:31 PM | Unregistered Commenterdave ward

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