PROCEEDINGS of the23rd International Congress on Acoustics
9 to 13 September 2019 in Aachen, Germany

A comparison of inaudible windfarm noise and the naturalenvironment noise whilst monitoring brainwaves and heart rate.
Steven COOPER1
1

The Acoustic Group, Australia

ABSTRACT
A pilot study undertaken in late 2017 using inaudible wind turbine noise and persons having aheightened sensitivity to turbine noise found the test subjects could detect the presence of the signal by
way of feeling (rather than hearing) the signal. A control group that had not been exposed to windturbine noise was unable to detect or sense the inaudible signal. A single case study as a precursor to afurther pilot study utilised inaudible wind turbine noise, inaudible white noise, inaudible surf (ocean)noise and an inaudible ventilation fan, was undertaken in a 126 m³ reverberation room and also in a 313
hemi-anechoic room, whilst monitoring of the test subject's heart rate and brainwaves was obtained.
The results of that testing are discussed.
Keywords: Wind Turbine Noise, Brain Response

1. INTRODUCTION
A common complaint from residents in proximity to wind farms is one of sleep disturbance andwaking up in an agitated state, where sometimes wind turbines may be audible and at other times theturbines are not audible.
Testing in 2017 [1] by the generation of inaudible full-spectrum signals of a high quality, highsample rate wave file recording of noise detected in the master bedroom of house 87 in the Cape
Bridgewater study [2] was presented to 2 groups of nine test subjects. One group involved people whohave been found to be sensitive to wind turbine noise who had either moved away/abandoned theirhomes or reside at a different place a number of times per week. The second group (control group) ha dnever been exposed to wind turbine noise.
Monitoring of wind turbine noise (both external to premises and inside dwellings) has revealed thepresence of a dynamically pulsed amplitude modulation [3] which involves a significant variation in
the overall pressure level where that variation occurs at an infrasound rate, being identified as theblade pass frequency. One common description used to describe this modulation for wind turbines is“amplitude modulation” The pulsation affects all frequencies and is not necessarily amplitude
modulation as defined in an electrical engineering sense (other than modulation of the tone associatedwith the gearbox output shaft) [4]. Utilising digital frequency analysis of the infrasound region reveals
a signal at the blade pass frequency and harmonics of that frequency.
Leventhall [5] has suggested the modulation of the low frequency components of wind turbine
noise may be the source of annoyance and not infrasound per se.
Basner and Greifhan [6] have suggested that monitoring of heart rate variability may be one tool forinvestigating sleep disturbance associated with wind turbines.
Due to relocation from premises containing the laboratory used for previous “wind turbine noisetesting”, and the need to consider reconstructing laboratories in a temporary location, an experimental
test of a one-person case study was undertaken to monitor the test subject's heart rate and brainwaves.
Seven different signals were being applied in two test rooms.

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drnoise@acoustics.com.au

2. METHODOLOGY
The test signals that were utilised for the experiment involved:x the Cape Bridgewater test signal (inside a dwelling) utilized in the previous study [1],x surf noise at a headland above ocean cliffs,
x three different samples of wind turbine noise obtained in the outside environment involving
different degrees of amplitude modulation,x noise of a large exhaust ventilation fan for an underground coal mine,x white noise, andx ambient noise prior to and after the seven samples.
The monitoring of the test subject for the seven samples (and the ambient noise) utilised eachsample having a time period of three minutes with all samples being inaudible to the test subject inboth test rooms.
The first room that was tested was a 126m3 reverberation room used in the previous studies where
all the internal walls and the roof are lined with 50 mm thick medium density polyester and the noise
emitter for the signal generation was twelve 15 inch 1000 watt (RMS) subwoofers fixed to a baffle of
two layers of 38 mm craftwood and three layers of 16mm plasterboard mounted in the aperture of thereverberation room.

Figure 1: Test set up in Reverberation Room
The frequency response of the subwoofers falls off after 1 kHz and thereby provides an effective
low pass filter to restrict the signal to the low/mid frequency bands and the infrasound bands. The
system is able to generate a clear sine wave at 1 Hz at a level of 96 dB.
The second room was a hemi-anechoic room where all walls and ceiling are subject of seven layersof insulation, with the first three layers being a high-density polyester (50 mm thick), followed by 50
mm thick glass wool insulation and three layers of 50 mm thick low density polyester. The anechoic
room as an empty room has a volume of 31 m3.
The speakers in the anechoic room involved three 12 inch subwoofer speakers in a sealed enclosureand three (vertical) line array speakers (28 o beam width for each array) positioned across the shortdimension of the room so as to create a uniform sound field with the capability of the line arrays togenerate frequencies up to 16 kHz.

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Figure 2: Speaker set up in hemi-anechoic room
The line array system in the hemi-anechoic room has been used for the evaluation of stereo versus
mono signals [1]. For the purpose of this study all three sets of line array/subwoofers had the same
signal (i.e. mono) generated across one end of the hemi-anechoic room.
The original signals for obtaining the sound files were recorded using a Bruel & Kjaer LANXI
Pulse Unit Type 3050-B-040, using GRAS 40AZ microphones and B & K 2669 preamps. The
recordings were obtained using B & K Pulse DATA Recording Module or B & K Connect with asample rate of 51.2 kHz rather than the typical 44 or 48 kHz rate, which has been found to be lackingin terms of reproduction of the pulsations associated with wind turbine noise and other transient noises[7].
As the acoustic signature of wind turbines contains a time varying stream of pulses occurring at aninfrasound rate, under the “fluctuation” definition from Zwicker & Fastl [8] the individual senses
rather than hears the modulation with the degree of sensing dependent upon the rate of thepulse/modulation and the depth of the modulation. Leventhall [5] refers to Bradley [9] who
investigated modulation at an infrasound rate of low frequency noise and found a similar result toZwicker & Fastl, but expressed the impact in terms of annoyance.
The four wind turbine signals contain amplitude modulation to varying degrees. The ventilation fan
has an infrasound pulsation whilst the surf noise and white noise have no periodic function.
The detailed narrow band and 1/3 octave band, time and frequency data for the seven signals(derived in accordance with the procedure in ref [4]) can be viewed from the following links(http://acoustics.com.au/media/ICA2019BW01andhttp://acoustic.com.au/media/ICA2019BW02.pdf).
Figure 3 presents the A-weighted Leq spectra (including the modulation indices) for the windturbine signals, whilst Figure 4 presents the ventilation fan (with modulation indices) versus the surf
noise and white noise (that have no modulation indices).

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Figure 3 – A-weighted 1/3 Octave Bands and Modulation Indices for the 4 Wind Turbine Samples

Figure 4 – A Weighted 1/3 Octave Bands an Modulation Indices Non-Wind Turbine Samples
However, in dealing with internal noise levels the attenuation of building elements renders the useof A-weighted spectra of little assistance. The use of Unweighted (linear) results (Figure 5) would
appear to be more appropriate for assessing fluctuations where higher amplitude modulation indicescan be seen.

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Figure 5: Figure 3 as Unweighted levels
The generated wave files were sent to multiple D Class 2000 watt amplifiers via ahigh-performance Schiit Gungnir DAC providing a 115 dB dynamic range analogue output from 1 Hz
to 100kHz (-1dB). The D class amplifiers had input compensation capacitors to provide a frequency
response from 0.5 Hz.
The audio signals were individually normalised to a 25 dB(A) source level then attenuated toachieve a contribution of 18 dB(A) for the reverberation room and 12 dB(A) for the hemi-anechoicroom, to be inaudible in both rooms.
For the levels that were generated, the testing was undertaken in accordance with AustralianStandard AS 1269.4 Occupational Noise Management, Part 4: Auditory Assessment [10] and thetesting conducted in accordance with the ASA Ethical Principles of the Acoustical Society of America
for Research Involving Human and Non-Human Animals in Research and Publishing Presentations[11]. An observer was present in each room during the testing.
The test subject was not aware during the testing of the type of noise source, or when the signals
were applied. The psychologist was given a 1 minute count down to the application of the test signals
but no information as to the content/type of the signals.
The heart rate monitoring used a Contec Medical Systems Dynamic EGG System Model TLC5000,
with the setup of the monitor conducted by a Registered Nurse.
The brain wave monitoring was conducted by a Psychologist who is an accredited BCIA Certified
Practioner using a J&J Neuronavigator. The test subject has been a patient of the psychologist for 11years, is familiar with the conduct of brainwave tests and would not exhibit any anxiety associatedwith the EEG testing.
The EEG data was run through a normative database to evaluate the nature of the severity ofderegulation in brain regions. The normative database used was the Dr Robert Thatcher Neuroguide
database (Applied Neuroscience Inc).
The QEEG (Quantitative EEG) provides information on impaired conduction and connectivity
between different areas and neural networks in the brain.

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3. OBSERVATIONS
The first set of tests in the 126 m³ reverberation room [12] were undertaken with the test subject in
the centre of the room in front of the sound field from the speakers, with eyes closed throughout theentire test.
The test subject was unable to detect any noise during the test program.

4. RESULTS
The subsequent post analysis of the data was examined with respect to the time of the applied
signals noted by the acoustician controlling the signal generation.
The heart rate monitor revealed variations during the different test samples.
The details of the EEG results are outside our area of acoustic expertise and will be the subject of aseparate paper by the psychologist. However, the results have been summarised for mere acousticians
as follows:
x The monitoring of the brainwaves revealed for the reverberation room test a posterior
dominated alpha frequency of 10 Hz with the overall amplitude remaining within two
standard deviations of the norm, except for the ventilation fan test. In terms of individual
brain monitoring sites, the Bilateral Medial sites (T3 and T4) were found to exhibit changes
depending upon the different (inaudible) signals.
x The increase in T3 and T4 exhibited during the noise samples remained at a steady rateduring the white noise and the baseline testing.
x Monitoring in the hemi-anechoic room after a 10 minute break for setting up equipment
found at the commencement of the testing that the fundamental posterior dominate alphafrequency of the test subject had reduced to 9.5 Hz and that by the end of the testing had
reduced to 8 Hz.
x For the same test signals in the hemi-anechoic room the EEG indicated levels exceeding 2
standard deviations with respect to the normative database. Noticeable increases in theBilateral Medial sites (T3 & T4) were observed and a significant increase in the Central
Midline site (i.e. Vortex Cz).

5. DISCUSSION
The consequence of having full-spectrum frequencies generated in the anechoic room revealed thaton a dB(A) basis the levels in the anechoic room were actually lower than in the reverberation room,
but the inaudible levels in the hemi-anechoic room had a significantly greater high frequency
component by reason of the frequency response of the speaker system being used.
The increased frequency response for the hemi-anechoic room suggests that for the same dB(A)level the presence of inaudible frequencies above 1kHz is relevant.
Subsequent comparisons of the same signals in the reverberation room (limited to 1kHz) toobservations in the hemi-anechoic room (by other test subjects) consistently gives rise to a greaterlevel of annoyance in the hemi-anechoic room by persons having a sensitivity to wind turbine noise.
The results of this single case study, when added to the pilot study [1] referred to above, suggeststhat persons with a sensitivity to turbine noise can experience changes in the EEG during the presenceof the signal or the operation of turbines, even when such noise is inaudible.
The changes in EEG and heart rate that were observed in the testing of the inaudible sound are an
automatic response of the body and cannot be attributed to the false claim of nocebo and as suchsupport the startle reflex concept previously considered [13].

6. CONCLUSION
Testing was undertaken as an extension of the 2017 double blind pilot study of inaudible windturbine noise to investigate whether heart rate monitoring or brainwave monitoring could identify a
response to the sample noise.
This one case experimental study is the result of six years of investigation into measuring and being
able to accurately create wind turbine noise for laboratory study (by others).
The testing found that there was a measurable impact under EEG monitoring to the test samples,
thereby supporting the hypothesis for undertaking further studies in this work for which funding isbeing sought.

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From this testing it is proposed:xxxxx

The testing could be undertaken using the existing test samples for one case study, or in theresident’s home and then repeated as on “on/off” test in the laboratory.
The testing utilize one test sample spectrum in a session with a nominal exposure of 20
minutes. Then the exercise be repeated with a different test sample.
A recovery time of not less than 30 minutes be applied if another sample signa l is to betested.
The study team should be expanded to include appropriate medical experts to undertake
additional testing to ascertain the components of the body responding to the test signal.
The testing involved immersing the test subject into the entire sound field and not justheadphones exciting the ears. Accordingly, testing of using just headphones could be ofbenefit in assessing whether the impact is a whole body experience or just the ears. .

ACKNOWLEDGEMENTS
The author needs to acknowledge the assistance of Rosemary Boon from Learning Discoveries, thepatience of staff at The Acoustic Group, and more importantly the patience and assistance of theauthor's family who have “enjoyed” some six years of private research and investigation, including
extensive long drives and field trips to various wind farms around Australia. However, those field trips
have led to meeting a wonderful group of rural residents who have offered the use of their premises foracoustic testing and then attended our laboratory to assist our research into wind turbine noise.

REFERENCES
1.

Cooper SE, Subjective perception of wind turbine noise – The stereo approach, Acoustical Society ofAmerica Meeting, New Orleans, December 2017, ASA POMA Vol 31/10.1121/2.0000653
2. The Acoustic Group, “The Results of an Acoustic Testing Program, Cape Bridgewater Wind Farm”,Dec
2014
http://waubrafoundation.org.au/resources/cooper-s-acoustic-group-results-cape-bridgewater-acoustic-i
nvestigation/
3. Cooper SE & Chan C, Wind Farm Infrasound – Are we measuring what is actually there or somethingelse? (part 3), Acoustical Society of America Meeting, Hawaii, December 2016
4. Cooper S, A simplified method for determination of "amplitude modulation" of audible and inaudible
wind turbine noise, ICA 2019, September 2019.
5. Leventhall HG. Benton S, A review of published research on low frequency noise and its effects, reportfor Defra, 2003
6. Griefhan B, Brode P, Marks A, & Basner M, “Autonomic Arousals Related to Traffic Noise during
Sleep, Sleep, Vol 31, No 4, 2008
7 Cooper S, Are Sample Rates for Wave File Recordings Too Low for Transient Signals?, AcousticalSociety of America Meeting, Boston, June 2017
8. Australian Standard AS 1269.4 Occupational Noise Management, Part 4: Auditory Assessment,
Standards Australia, 2005.
9. Bradley J.S., Annoyance caused by constant-amplitude and amplitude-modulated sounds containing
rumble, Noise Control Engineering Journal 42 (8) 1994
10. Australian Standard AS 1269.4 “Occupational Noise Management, Part 4: Auditory Assessment”,
Standards Australia, 2005.
11 Acoustical Society of America, “Ethical Principles of the Acoustical Society of America for Research
Involving Human and Non-Human Animals in Research and Publishing and Presentations”,
http://acousticalsociety.org/for_authors/ethical_principles
12 Cooper SE, Subjective perception of wind turbine noise, Acoustical Society of America Meeting,Boston, June 2017, ASA POMA Vol 30/10.1121/2.0000639
13. Cooper S E, Can inaudible and audible low level infrasound and low frequency noise be an
acoustic trigger of the startle reflex?, Acoustical Society of America Meeting, Hawaii, December
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