“But wind turbine noise issues are not just an acoustic issue. I have been trying to solve the acoustic problem to allow the medical side to then undertake the required research.” (Cooper, below)
Last year, I interviewed acoustician Steven Cooper, AU on wind turbine health issues related to pulsation and low-frequency noise. “In general, wind farm applications claim that turbines do not generate any low-frequency, tonal, or impulsive characteristics,” he noted, “which is a matter disputed by residential receivers.”
What has developed in the last 20 months? In this two-part series (today and tomorrow), Mr. Cooper shares his most recent research and findings, which complement our current knowledge regarding the nature of “noise” impacts to real-time victims of wind power.
Mr. Cooper recently presented his new findings in Germany at the International Congress on Acoustics Conference. As Mr. Cooper states in this interview:
“I question how an authority can propose noise criteria with no fundamental basis identified as to how a stated core objective can be satisfied.”
Q: Since our previous discussion for Master Resource you have continued your research into the basis of wind-turbine noise. Your presentations to the Acoustical Society of America in December 2017 and Euronoise in May 2018 presented the results of your testing of inaudible wind-turbine sound on a group of people who have been severely impacted by turbine noise to the extent of regularly leaving or permanently leaving their home, versus a group of people never been exposed to wind turbine noise.
Q: You still seem to be pushing boundaries and asking fundamental questions on what is the “signature of wind turbine noise.”
Cooper: Correct. As a noise engineer you have to understand what is causing the problem before you can arrive at a solution. But wind turbine noise issues are not just an acoustic issue. I have been trying to solve the acoustic problem to allow the medical side to then undertake the required research.
Q: Congratulations are in order as you have been appointed to the European Acoustics Association Technical Committee on Noise as the group leader on wind turbine noise, and last month gave three papers at the International Congress on Acoustics in Germany.
Cooper: Right. The papers were well received and led to multiple discussions with individual experts during the conference. The three papers and a pdf of the power point for each paper are up on National Wind-Watch, two in the acoustics section and one in the general section.
Q: In our previous interview for Master Resource you identified a series of relatively simple questions in relation to criteria to protect against sleep disturbance that need to be answered by Regulatory Authorities. Any response?
Cooper: No. Still a deafening silence. Also on Wind Watch is my submission on a review of draft wind farm guidelines for South Australia that refers to those questions. I question how an authority can propose noise criteria with no fundamental basis identified as to how a stated core objective can be satisfied.
Q: Previously we have discussed that you don’t use the term ILFN (Infra and Low Frequency Noise). I have trouble getting my head around that. Your position on ILFN seems to cause some problems for people in discussions on wind turbine noise. When discussing infrasound from turbines you have referred to the infrasound signature showing peaks in the spectrum being multiples of the blade pass frequency. Why this specific terminology?
Cooper: I have never used the term of infrasound sound. I used “infrasound signature” to refer to the result of a frequency analysis. This is because the noise from a turbine has a broad band signal with some tones associated with the gearbox, but the time signature of the pressure signal from turbines is a series of pluses that occur at an infrasound rate. The pulses are very short in time when compared to the wavelength of the blade pass frequency and are not of a continuous nature like an audible sound. You can use FFT analysis to show the presence of an operating wind turbine.
Q: The term FFT is used in wind turbine noise, and you reference it here. What does it mean?
Cooper: FFT stands for Fast Fourier Transform. It is a method used in digital analysis to extract the periodic functions in a time signal to derive a frequency spectrum. It is the modern way of creating narrow band analysis.
This form of analysis is the basis of the “infrasound” problem. The FFT procedure identifies the occurrence of the presence of the pulsations in the time domain (say every 1.2 seconds) which is at the blade pass frequency (0.86Hz), because they are a periodic function. That doesn’t mean there is a constant sound at 0.86 Hz. (For those wishing a more detailed explanation, we request you contact Master Resource for the email of Mr. Cooper.)
Q: As a result of your research you have produced a number of presentations in relation to the acoustic signature of wind turbine noise and have questioned the issue of infrasound being an actual sound signal.
Cooper: Correct. For the ASA (Acoustic Society of America) wind turbine working group I have given a number of presentations on the question of there being infrasound present in the acoustic signature. In our quest to accurately reproduce the wind turbine signal for subjective testing we found real issues in the frequency response of speakers/amplifiers, but as presented to the ASA in Boston we also found issues with the analysis of the pulses. We could remove all frequencies being sent to the speakers below 50 Hz and the infrasound signature was still present. There are fundamental technical issues for analysis that are not met by the short duration pulses in that what is being assessed are the pulsations of the signal, not actual infrasound.
Q: So if I understand this correctly you are saying you can take the wind turbine signal that in a normal frequency analysis shows peaks at the blade pass frequency (say 0.86 Hz) and multiples of that frequency, and reproduce that signal in a laboratory that can go down to 0.5 Hz. But having a filter to block out all the infrasound going to the speakers, you still get a frequency analysis of that sound still shows peaks in the infrasound region.
Cooper: Yes. Because the analyser is providing the results of the overall sound levels varying (modulating) at an infrasound rate.
Q: Well that concept may be giving me a headache. But that would be in my head. And this leads me to the nocebo concept, that wind turbine impacts are psychosomatic, proposed by Simon Chapman, and that it is all in people’s heads. You say he is right in one sense but wrong in another.
Cooper: Yes. In the New Orleans ASA and the Euronoise presentations we identified that the sensitive people were able to sense the operation of the signal (even though it was inaudible) and the majority of the sensitive group identified feeling it in their head (our emphasis). In the brainwave paper at the ICA for a test case we showed the inaudible signals affected frontal lobes. So it is right that people can sense the signal but not in the concept proposed by Chapman that they are making it up. The amplitude modulation paper goes to the work of others in relation to sensing the modulation.
Q: I see that some acousticians quote the work of Crichton as setting the bar on establishing the nocebo concept.
Cooper: Yes, and there is a problem with acousticians accepting that data without examining the material. If you look at the ICA (International Congress on Acoustics) synthesis paper (now on National Wind Watch) and more importantly, from slides 6 & 7 of the PowerPoint you will see that the basis on the Nocebo proposed by Crichton is flawed.
Despite the title of Crichton’s paper she never used what has been identified in frequency analysis as “infrasound” for wind turbines. Look at the title of the paper then look at her signal. She used a single tone (see slide 6). I have never seen a single tone at 5 Hz (or 9 Hz) from wind farm.
The figure slide 7 of the PowerPoint superimposes Crichton’s “infrasound signal” onto the Shirley wind farm graph provided by Walker, Hessler & Hessler, Rand, and Schomer. That frequency graph is typical of a narrow band frequency analysis of a wind turbine. Also note the orange line is the manufacturer’s specification for the speaker used by Crichton that would seem to have some difficulty producing the “wind turbine infrasound” used in the experiment.
Furthermore, if you look at Crichton’s PhD thesis (on this work), one of her supervisors was Simon Chapman.
Q: The synthesis paper raises further issues with using just wind turbine infrasound and creating a digital signal for subjective assessments of wind turbine noise.
Cooper: Yes. If the synthesised “infrasound” wind turbine levels are well below the threshold of hearing for actual infrasound sounds and don’t produce the same time signal pressure variation as in the real world, and leave out the rest of the wind turbine signal that is in the normal audible range of sounds, then why use such signals – particularly when you have a US Standard for wind turbine (Annexure D of ANSI/ASA S12.9-2016/Part 7 “Advanced Signal Processing Techniques”) providing caution on using a signal that may have the same energy but sounds different.
Q: Your Cape Bridgewater study took a fair time to digest and comprehend. I think people may need a fair bit of time to digest this new information and carefully read the paper and also view your PowerPoint.
Cooper: Yes. This is what happened in Germany. Quite a few esteemed acousticians later in the week came to have a one-on-one session with me. I hope people will take the time to explore my clarification of this complex issue. We still do not have government authorities or wind developers being required to explain any of the impacts, nor protect people from such impacts.
For example, in Australia we still do not have the Authorities or the Wind Farm Commissioner providing noise criteria for wind turbines that is based on actual measurements/studies that identify noise levels that will not give rise to sleep disturbance. As these issues are relevant to the three ICA papers my submission in relation to a draft noise guideline in Australia is also on Wind Watch here. A review of that paper will place in context my material presented at the ICA.
Please watch for tomorrow, part two of this interview. Mr. Cooper’s second paper is even more technical. Comments regarding Crichton and Chapman are referenced here, as both persons have denigrated the impacts, claimed they are NOCEBO (in people’s minds, psychosomatic), and have significantly dampened and in our view, polluted, the real conversation about wind turbine harms. See here.