Content uploaded by Geoff Leventhall
Author content
All content in this area was uploaded by Geoff Leventhall on May 20, 2017
Content may be subject to copyright.
www.SandV.com34 SOUND & VIBRATION/JANUARY 2017
Health Effects from Wind Turbine Low
Frequency Noise & Infrasound
Do Wind Turbines Make People Sick? That is the Issue.
Do wind turbines make people sick? That is a contentious is-
sue in licensing wind farms. In particular, low frequency sound
emissions (infrasound and “pulsed” and steady low frequency
sound) from wind turbines are blamed by opponents but vigor-
ously denied by project proponents. This leads to an impasse of
testifying “experts,” and regulators must decide on the basis of
witness credibility for each project, leading to inconsistent find-
ings. This article presents the opinions of four very experienced
independent investigators with wind turbine acoustics over the
past four decades. The latest Threshold-of-Hearing research down
to 2 Hz is compared to today’s modern wind turbine emissions. It
is jointly concluded that infrasound (0-20 Hz) can almost be ruled
out, subject to completion of recommended practical research, and
that no new low frequency limit is required, provided adequate
“A”- weighted levels are mandated.
Claims of adverse health effects are made by individuals and
organized community groups at some operating wind turbine sites
located around the world. Adverse publicity is intense at about a
dozen operating sites in the United States, the United Kingdom,
Canada, Scandinavia and Australia. Health effects attributed to
wind turbines include symptoms similar to those of motion sick-
ness, such as, dizziness, nausea, vomiting and a general feeling
of discomfort or not feeling well. Sea sickness (a form of motion
sickness) is well understood as a disturbance of the inner ear, and
the cause is both obvious and indisputable. Motion sickness is more
subtle and is caused by the brain receiving conflicting messages
about what is seen by the eye as opposed to what is felt or sensed.1
For example, air sickness can result from plane motion caused by
invisible turbulence in the air. To date, no such similar connection
has been found at wind turbine sites, although some residents claim
they can sense when wind turbines become operational without
benefit of sight or hearing.
It has now been demonstrated by multiple independent re-
searchers that wind turbines, like any other rotating fan, emit
measurable tones at the blade-passing frequency (BPF) and up
to about the fifth harmonic plus broadband noise. For a typical
large three-bladed wind turbine rotating at 16 RPM, the BPF and
harmonic tones are at frequencies of 0.8, 1.6, 2.4, 3.2, 4 and 4.8 Hz.
These very-low-frequency tones are commonly called infrasound,
defined as low-frequency noise in the 0-20 Hz frequency range.
A better definition used by one of the authors is “pulsed LFN,”
since the tones result from analysis of pulses produced by tower
blade interaction. The 0-20 Hz measurements are all well below
the threshold of hearing, as established by the latest research at
frequencies down to about 2 Hz. But it might at least be asked: Are
the pulses the invisible source of conflicting messages to the brain?
Reference 1 states that messages “are delivered from your inner
ear, your eyes (what you see), your skin receptors (what you feel)
and muscle and joint receptors,” but there is the open question
of whether the low levels of pulsed LFN or infrasound from wind
turbines excite any of these receptors.
Permitting authorities for new projects must evaluate adverse
health effect claims presented as proven factual data by opposi-
tion forces, countered by project advocates that state no physical
link to health effects has ever been demonstrated at wind turbine
sites. This debate has now raged for at least a decade and is now
at an impasse.
It has been the first author’s privilege and pleasure to associ-
ate and collaborate with three prominent co-author scientists in
the wind turbine acoustical field. All four authors do not doubt
for a moment the sincerity and suffering of some residents close
to wind farms and other low-frequency sources, and this is the
reason all four would like to conduct, contribute or participate in
some studies that would shed some light on this issue. It must also
be said that it is human nature to exaggerate grievances and that
some qualitative measure must be made available to compensate
affected residences.
The first author has asked each co-author to independently sum-
marize their opinions and recommendations on how the current
impasse can be broken.
Current Research on the Threshold of Hearing
Research to measure the threshold of hearing at low frequencies
can be summarized in one graphic (see Figure 1). The highest and
lowest gray bars encompass the results of 10 studies over the listed
30-year period that is nicely shown in the Noise & Health Journal.2
These are the min. and max. at each 1/3-octave-band frequency for
any of the 10 studies. The graphic also plots ISO 226:2003(E) that
covers the entire audible range from 20 Hz to 12,500 Hz (plotted to
1000 Hz). The green line comes from Project EARS funded by the
George Hessler, George Hessler Associates, Inc., Haymarket, Virginia
Goeff Leventhall, Consultant., Ashtead, Surrey, United Kingdom
Paul Schomer, Schomer and Associates, Inc., Champaign, Illinois
Bruce Walker, Channel Islands Acoustics, Camarillo, California
Figure 1. Research summary for determining threshold of hearing at low
frequencies.
www.SandV.com 50th ANNIVERSARY ISSUE 35
European Union3 and represents “acceptance levels” based on the
10% percentile hearing threshold values determined in the EARS
Project and is the latest research on the subject.
Defining the Problem
How does ILFN from a modern wind farm compare to the above
summary? Figure 2 replots the contents of Figure 1, all in blue,
and adds the measured spectra and overall levels at three loca-
tions from a study4 funded by Clean Wisconsin (an environmental
organization) and the state of Wisconsin. This study was carried
out at a wind farm located among residences in a quiet environ-
ment of residences and farmland, typical of wind farm sites in the
American midwest and northeast. Response at this site has been
adverse, to say the very least. The three plots are near residences
reported to be abandoned due to adverse health effects. Several
things may be deduced form this plot.
First, the wind farm was designed to a standard of 50 dBA at
nonparticipating residences, and that level is not endorsed by any
of these four authors. All of us have been at or near 40 dBA for many
years. Had 40 dBA been used, there would not be a wind turbine
as close as 1100 feet at R2, where a level of 48 dBA was measured.
Wind turbine sound was readily detectable by the test engineers
at R2, but not at R1 and R3 where levels are less than 40 dBA.
Second, the levels at all the residences in the infrasound range
(0-20 Hz) are far below perceptible levels in this range. This
strongly suggests the source of any message to the brain is not
from wind turbine infrasound directly but may occur as audible
LFN or pulsing LFN at the blade-passing frequency well inside
the infrasound range.
Third, a wind turbine is not a classic LFN noise source – a
source heavily weighted with LFN. Such sources typically have
C-weighted levels 15 or 20 dB above A-weighted levels. Observe
from the plot that C-weighted levels are both relatively low (<60
dBC) based on typical C-weighted guidelines, and the C-A differ-
ential is less than 15 dB.
To understand just how difficult this issue is, consider that the
residents (husband, wife and young baby) at R2 experienced their
child awakening at night screaming, but not on nights away from
home. The wife was highly annoyed, and the husband had “no
problem at all” with wind turbine sound. Add to this that there
is a home across the street, the same distance and direction from
the turbine, but the owners accept “good neighbor” payments.
Could any payment be enough if suffering serious health effects?
And last, there are thousands of landowners that lease their
land for wind turbines and live very close to turbines. It is hard to
abandon the notion that higher levels closer to the source should
produce higher levels of affected residents, but a recent large-scale,
long-term measurement survey in Australia showed no correlation
between complaint locations and measured levels.
It would seem one promising direction of a study could be
extensive interviews of such folks exposed to high levels of wind
turbine noise that could reveal common symptoms and/or the
number of folks seriously affected.
Opinions and Recommendations of Geoff Leventhall
Wind Turbine Noise and Health. Wind turbine noise spans a
range from below 1 Hz up to 10 kHz or more. A one-third-octave
spectrum typically drops off at between 4 dB/octave and 6 dB/
octave. Blade-passing tones are added into the falling spectrum in
the range from about 1 Hz to 7 or 8 Hz and have normally disap-
peared from the spectrum by 10 Hz, although they may reappear
at a low level at higher frequencies. (Zajamšek, Hansen et al.
2016). The high correlation between wind turbine dBA and dBC,
(Keith, Feder et al., 2016) is explained by this generalized falling
spectrum from infrasound to high frequencies, also described by
Tachibana et al., who found 4 dB per octave fall-off (Tachibana,
Yanob et al., 2014).
Sound level at nearest residential distances of, say 500 m, may
be around 60 dB at 10 Hz, while the hearing threshold is close to
100 dB at this frequency. A falling spectrum of 6 dB/octave (20
dB/decade) gives 80 dB at 1 Hz for a level of 60 dB at 10 Hz. The
hearing threshold is not well known at 1 Hz but is likely to be about
130 dB, since measurements have shown a threshold of 120 dB at
2.5 Hz (Kuehler, Fedtke et al., 2015)
Levels of wind turbine infrasonic blade tones are well below
our normal hearing threshold, while at higher frequencies, say
30-50 Hz, the blade harmonics, if present, may approach median
threshold. (Zajamšek, Hansen et al., 2016).
Wind turbine sound fluctuates due to short-term variations in
propagation, with typical maximum fluctuations of about 15 dB
(Bray and James 2011). Wind turbine low-frequency noise normally
becomes just audible to the average listener at frequencies above
40-50 Hz. Higher audible frequencies, 250-1000 Hz from aero-
dynamic noise may vary in level at the blade-passing frequency,
giving amplitude modulation (swish) of about once per second.
Frequencies in the higher kilohertz range are heavily attenuated
by air absorption and are not normally a factor in wind turbine
noise at residences.
Does wind turbine noise, as experienced at typical residential
distances, affect health through either direct or indirect mecha-
nisms? There is wide variation in human response to audible
noise, especially to low levels of noise like that produced by wind
turbines, but these low levels are not known to have direct and
adverse physiological effects on the body. The term “physiological
effects” must be used carefully, since any response to a stimulus
is a physiological effect. The great majority of these responses are
harmless, beneficial or essential to our proper functioning.
Figure 3 shows a simplified diagram of the hearing process,
Figure 2. Typical wind turbine spectra and levels compared to threshold of
hearing at low frequencies.
Figure 3. Response process (left) and range of responses (right).
Response
Perception
Detection
Input
Aggressive resentment
Vocal nonacceptance
Aggrieved acceptance
Reluctant acceptance
Passive acceptance
www.SandV.com36 SOUND & VIBRATION/JANUARY 2017
leading to perception and response to a noise (Leventhall 1998).
Input noise is detected, stimulating perception via the auditory
cortex. Response, the reaction to perception, is very variable, as
in Figure 1, depending on many personal and situational factors
and conditioned by both previous experiences and current ex-
pectations. Response to the same noise from within a large group
might range from passive acceptance (I can hear it, but it does not
bother me) to aggressive resentment (I can’t stand this noise – it’s
ruining my life).
Daytime disturbance by noise leads to irritation and aversion,
while sleep disturbance may be an additional night effect, although
investigations have shown similar numbers of poor sleepers and
good sleepers both close to and remote from wind turbines (Nis-
senbaum, Aramini et al. 2012) (Jalali, Nezhad-Ahmadi et al. 2016)
(Michaud, Feder et al., 2016). Cognitive behavioral therapy reduces
disturbance from noise through a process of desensitization and
can improve sleep and quality of life (Leventhall, Robertson et
al., 2012).
The main effect of low levels of unwanted audible sound is
creation of hostile reactions and negative thoughts, leading to
stress and to the adverse health effects that might follow. Stress
has different intensities, ranging from cataclysmic events (war and
earthquakes), to acute personal stress (bereavement), and to chronic
low level stress (long-term illness or persistent personal problems)
(Benton and Leventhall, 1994). Stress from wind turbines, if it
arises, is normally low level but, in a very small number of people,
it may become intense and overpowering so that opposition to wind
turbines is the dominating emotion in their lives. Unfortunately,
concentrating attention on an unwanted noise aggravates any prob-
lems. Anticipatory stress also occurs following approval of a wind
farm, although it has not yet been built, and a few anxious residents
may experience similar symptoms to those that they believe to be
associated with an active wind farm (Mroczek, Banas et al., 2015).
Reaction to noise, especially low-level noise, is largely con-
ditioned by attitudes to the noise and its source. Noise level
contributes only about 20-30% of the total annoyance from noise
(Job, 1988), while feelings, fear and opinions shape many of our
responses, influencing tolerance levels. Negative emotions give an
additional impact to an unwanted stimulus. The attitudes of nearby
residents toward wind turbines is a major factor in the effects that
turbines may have on their health (Rubin, Burns et al., 2014). It has
been shown that sham exposures to infrasound, (Crichton, Dodd
et al., 2014) or to sham electric fields (Witthoft and Rubin, 2013)
produce symptoms in those who have been primed to expect an
effect from exposure. The human being is clearly very complex in
its reactions to physical and psychological stimuli.
Infrasound has a special place in discussions of the health effects
of wind turbines, with many claims centered on direct pathological
interactions, initially fostered by media scare stories originating in
the 1960s and still continuing (Leventhall, 2013a).
In his 1974 popular science book Supernature, Lyall Watson
described infrasound as causing deaths (“fell down dead on the
spot”), while focused infrasound “can knock a building down
as effectively as a major earthquake.” This is unfounded, but an
aura of mystery and danger persists around infrasound deep in
the minds of many people, where it waits for a trigger to bring it
to the surface. A recent trigger, heavily manipulated by objectors
and media, has been wind turbines (Deignan, Harvey et al., 2013).
A concept from psychology is the “truth effect,” which explains
how we can develop belief in false statements through their repeti-
tion by others (Henkel and Mattson, 2011).
• We believe statements that are repeated, especially by different
sources.
• The path to our belief is made easier by each previous repetition.
Advertising and political propaganda are clear examples of the
operation of the truth effect, which is also known as “illusory
truth.”
We all also have our preferred beliefs. When there is a choice,
we tend to believe what we wish to believe. We feel comfortable
when our existing beliefs are confirmed, and if we have become
antagonistic to wind turbines we readily absorb negative state-
ments about them.
Some objectors to wind turbines further their cause by generat-
ing anxiety on effects on health, particularly from infrasound and
low-frequency noise, in populations close to proposed wind farms.
Persistent repetition that infrasound from wind turbines will cause
illness develops stressful concerns in residents, but repetition is
neither evidence nor proof. However, a nocebo effect may occur,
by which expectation of an outcome may lead to realization of that
outcome (Chapman, Joshi et al., 2014).
There are a large number of coordinated objector groups working
internationally. A web page (https://quixoteslaststand.com/) gives
links to more than 2000 groups that share information on wind
turbines, while some make unsubstantiated, anecdotal claims about
their effects. However, there is no doubt that when stress is persis-
tent it may result in somatic effects in a small number of people
who have a low-coping capacity, although the ability to cope can
be enhanced (Leventhall , Robertson et al., 2012).
In considering infrasound and other sound from wind turbines,
it is necessary to take a very analytical, critical, unemotional view
of the topic and to remain free of the influence of incorrect, but
frequently repeated, statements.
There is no evidence that inaudible infrasound from wind tur-
bines affects health, but there are indications from exposure tests
that it does not (Tonin, Brett et al., 2016). Inaudible infrasound has
not been shown to affect those exposed, but just audible infrasound
has a sleep-inducing effect (Landström, Lundström et al., 1983).
Comparisons have been made of levels of infrasound from wind
turbines at dwellings with the levels of infrasound that occur from
man-made sources in urban and industrial areas and also levels
that occur naturally in coastal and other regions. The infrasound
exposure levels are similar (Turnbull, Turner et al., 2012).
There is a persistent microbarom frequency of about 0.2 Hz
caused by interacting sea waves, which goes to high levels dur-
ing storms, propagating long distances over land. Microbarom
six-hour averages have been measured in the region of 60-70 dB,
while power spectral densities as high as 120 dB at 0.2 Hz have
been observed (Shams, Zuckerwar et al., 2013). We are not affected
by this infrasound, which is at higher sound pressure levels than
wind turbine infrasound at 0.2 Hz.
Investigations to find a link between infrasound from wind tur-
bines and adverse physiological effects include work by Salt, who
used high-level 5-Hz infrasound to bias the hearing of guinea pigs
and noted that the outer hair cells (OHC) responded to this stimu-
lus. The response threshold was lower than the hearing threshold,
which is determined by the inner hair cells. Salt used the single
measurement as a point on an OHC threshold curve and deduced
an OHC threshold for humans by considering the low-frequency
mechanics of the ear and comparison of human sensitivity with
guinea pig hearing sensitivity. The human OHC threshold was
determined as 100 dB at 1.0 Hz, falling by 40 dB/decade, so that it
meets the inner-hair-cell threshold at about 100 Hz (Salt and Hullar,
2010). They conclude: “The fact that some inner ear components
(such as the OHC) may respond to infrasound at the frequencies
and levels generated by wind turbines does not necessarily mean
that they will be perceived or disturb function in any way. On the
contrary though, if infrasound is affecting cells and structures at
levels that cannot be heard, this leads to the possibility that wind
turbine noise could be influencing function or causing unfamiliar
sensations.”
Wind turbine emissions are generally below the OHC threshold
so that, under these circumstances, the threshold is not relevant to
wind turbine infrasound. The effects of stimulation of the OHCs
remain unknown. The OHCs are the main component of the
cochlear amplifier and are continuously active, being the source
of otoacoustic emissions (Ashmore, Avon et al., 2010). But wind
farms at which nausea and similar effects are reported, may have
a spectrum that is entirely below the Salt OHC threshold, so that
it is not exceedance of this threshold that is the cause of distress.
Salt’s further publications, seeking to support the adverse effects
of infrasound, use examples in which the frequencies and levels
are higher than those from wind turbines (Salt and Lichtenhan,
2014). As pointed out by Dobie, Salt and Lichtenhan, quote ef-
fects resulting from 30 Hz at 100 dB and 120 dB and from 50 Hz
www.SandV.com 50th ANNIVERSARY ISSUE 37
at 85-95 dB (Dobie, 2014). These low-frequency pure tones are not
directly relevant to wind turbine noise, which does not contain
such high-level tones. Salt’s connection of his work to wind turbine
infrasound is not yet convincing.
Over the past 45 years, popular culture has attributed a number
of unpleasant, even fatal, effects to infrasound, but none has been
sustained by evidence. Concerns on inaudible infrasound from cur-
rent designs of wind turbines commenced 10-15 years ago, linked
to objections to the growth of wind farms, and have accelerated
over the past 5-10 years. It is inevitable that, in the absence of
good supporting evidence, these speculative claims will become
discredited over the next 5-10 years.
At the present time, conclusions are:
• Audible wind turbine noise acts through annoyance and stress,
which may lead to poor sleep quality, especially in hostile
people. Hostility is heightened by the actions of objector groups.
There is no known direct effect on health from the low levels of
audible wind turbine noise. However, stress may develop from
an individual’s reaction to the turbines.
• There is no established evidence that the inaudible infrasound
from wind turbines affects health, but there are indications that
it does not.
Opinions and Recommendations of Paul Schomer
Currently, I think this group of four find ourselves in the follow-
ing situation: We all agree that sound flowing through the cochlea
is not the source of problems below the threshold of hearing. That
statement leaves two of what I will call technical possibilities. One
possibility is that there are pathways other than through the cochlea
for the infrasound to get to the brain. A second possibility is that
to date we have missed something in the audible sound range that
is the source of problems or that both of these situations exist.
Are There Noncochlear Paths for Infrasound to Reach the
Brain? The following is a relatively simple study that could test
whether individuals who claim they can detect the turning on
and off of turbines can actually do this without visual or audible
clues. There are at least a few small groups in the United States,
Australia, and Canada that claim to have this ability. The results
could be that none of these people could detect the turning on
and off, or it could be the reverse and everyone would be able to
detect the turning on or turning off. It is likely that the result will
be somewhere in between.
In Shirley, Wisconsin, there are residents who say they have this
ability. This study could be readily performed in Shirley; however,
it requires the cooperation of the energy company.
Suggested Test 1
Consider the two houses in Shirley where there is no audible
sound; the R-1 house and the R-3 house. The residents of the
houses, and others, who would be subjects, would arrive at the
house with the wind turbines off. The test itself would likely take
0.5 to 2.5 hours to perform.
Sometime during the first 2 hours, the wind turbines(s) that had
been designated by the residents as the turbines they could detect,
might or might not be turned on. It would be the residents’ task to
sense this “turn on” within some reasonable time designated by the
residents – say 10 or 30 minutes. Correct responses, “hits,” would
be correctly sensing the turbines being turned on, or sensing no
change if they were not turned on. Incorrect responses, “misses,”
would be failure to sense a turn on when the turbines were turned
on, or “false alarms” would be sensing a turn on when the turbines
were not turned on. Similar tests could not necessarily be done
starting with the turbines initially on because the subjects, when
sensitized, find it more difficult to sense a turn off. More informa-
tion about this test can be found in Schomer et al., 2015.
Possible Overlooked Audible Path. This pathway is predicated
on several key facts described below. The main hypothesis is that
the electric power being generated changes the acoustic signal
without changing the A-weighted level. If the electric power cor-
relates better than A-weighted level to subject response, then this
would indicate that the electric power being generated controls
some aspect of the sound that the subjects are sensing. This is
important for two reasons:
• The subjects are incapable of having detailed knowledge of
the electric power.
• If this is all true, it is something that is potentially correctable.
Facts:
• Discussion with Geoff Leventhall. At one point when I sug-
gested to Leventhall that 30 and 40 years ago, the reported
effects were very similar to today’s reported effects and that we
had much the same problem, he remarked that the sound at that
time period was low-frequency audible sound at around 40-50
Hz. The problems with infrasound and low-frequency noise
that occurred 30 and 40 years ago is that they produce the same
symptoms as today, but were for frequencies in the 40-50 Hz
range – not infrasound.
• Steven Cooper. Cooper finds and reports in his Cape Bridge
Water Study that the subject’s response correlated better to the
electric power being generated, to turbine operations hovering
around cut in speed, and to large changes in the electric power
being generated rather than to the acoustic signal.
• Bruce Walker. “I did a lot of work with Hansen’s cleanest data
set. When the extremely narrow band spectrum was plotted on
a linear frequency scale, it conformed pretty well to sin(x)/x
envelope with lobes at ZF, 30 and 45 Hz (more or less) and lines
every blade-passing frequency. The lines in the 45 Hz lobe would
combine into a wave packet that exceeded the audible threshold
briefly once every blade pass. Walker added, “One thing I’ve
observed with modern 100-meter rotors is that when producing
power, the blades deflect axially to pass pretty close to the tower
near the tip, into a region where the upstream flow deficit could
be significant, though not separated as in downwind designs.
Overly aggressive pitch programming could cause periodic brief
stalls that might produce the requisite steep edge on the pulses.”
• Discussions at the ASA meeting in Salt Lake City. Discussions
at the meeting made it clear that the frequency may not be
limited to 45 Hz but may be based on the manufacturer and the
specifics of the blades. It was also suggested that these frequen-
cies might interact with chest cavity resonances. Rainford and
Gradwell (2012) find, using their procedure outlined in Rainford
(2006) that the typical chest cavity has a resonance at about 50
Hz. This does not seem to be a factor, since Leventhall reports
that below 80 dBA, at 50 Hz there is no chest cavity response.
• George Hessler. The measurements at Shirely show a relatively
constant noise being generated during the day and time of the
R2 measurements. However, the measured acoustic level was
1.5 dB below the expected level for full power with a Nordex
N-100/2500 wind turbine, the turbine used at Shirley. Nordex
literature reports that the acoustic output of the N-100/2500 is
a constant for wind speeds measured at a height of 10 meters.
At a wind speed of 4 m/s, the Nordex sound level is down
about 1.0 dB from the maximum. Wind turbine noise vs. wind
speed plots are unusual. As the wind speed increases from 0, it
reaches a speed where the rotors of the turbine can start to turn.
From this point, the noise from the turbine begins and goes
up rather rapidly with increasing wind speed until it reaches
a transition plateau where the sound level no longer increases
with wind speed. However, the power generated by a wind
turbine goes up much more gradually in power as a function
of wind speed and only reaches its maximum several meters
per second above the acoustic limit. The result is that for a very
small change in sound level generated by the wind turbine, there
can be a very large change in the electric power generated. This
is true for the Nordex N-100/2500. Table 1 is compiled from
Nordex literature and gives the relationship shown between
acoustic power emitted and electrical power generated as a
function of wind speed.
• Geoff Leventhall. Leventhall reports that the highest reaction to
low-frequency sound occurs in the 40 to 50 Hz range. However,
his data (Figure 4) show almost equal responses in the 30 to 40
Hz range and the 70-80 and 80-90 Hz ranges.
• Shirley Report. The Shirley report shows levels of 25-30 dB in
the 40-50 Hz range, and it shows room resonances and possibly
some wall resonances. Room resonances are in the 35-100 Hz
www.SandV.com38 SOUND & VIBRATION/JANUARY 2017
range. Wall resonances are typically in the 10-30 Hz range.
• Threshold of Hearing. The pulses, roughly one per second, that
result from the blades passing the support tower, appear to
have about a 10% duty cycle and would drop the threshold of
audibility by about 8 to 10 dB. Figure 1 shows threshold of
audibility based on several sources along with the lowest and
highest levels of audibility at a given frequency. These levels
are for continuous sinusoidal signals. With a 10% duty cycle,
the thresholds go down by about 9 dB. For the most sensitive
subjects, this indicates a threshold of hearing of about 31 dB at
50 Hz to 35 dB at 40 Hz.
• Bruce Walker. Bruce Walker’s findings that the tone at 45 Hz was
above the threshold of hearing stands in support of the theory
that low-frequency audible sound exists in the vicinity of wind
turbines and could be the source of problems. There is a pos-
sibility that these offensive signals can only be found using
narrow-band analysis as Walker used. Constant bandwidth
filters may be too broad.
• Steven Cooper. It is somewhat amazing that Cooper’s findings
fit this situation so well. He found that the peoples’ responses
correlated to large changes in electric power, turbine operations
hovering around a cut in speed, and the absolute level of the
electric power being generated better than to the acoustic level.
Table 1 supports Cooper’s findings. The electric power changes
gradually until full power is reached; the acoustic signature
rises quickly and then becomes a constant. Please note that the
subjects could know when the turbine was on or off, but the
data in Table 1 clearly shows that there is no way to know what
percent of the maximum electric power is being generated from
any data available to the subjects. So the fact that the subjects’
responses correlated with the electric power, which is some-
thing the subjects could have no way of knowing, lends strong
support to Cooper’s findings. The acoustic data during “large”
transitions in percent of full electric power should be analyzed,
since it could be a potential source of problems.
• The Energy Company. Clearly, it would be nice to have trustwor-
thy confirmation of this analysis. To date, the power company at
Shirley has not given any clear data on the actual power gener-
ated (or any other physical parameters, such as blade rpm, wind
speed, or direction) for any time during our measurements.
So we are limited to the indirect analysis of estimating a large
change on the basis of a 1 dB acoustic change.
This all suggests that the Shirley signals would be slightly too
low to trigger this chain of reactions. There are at least two pos-
sibilities. One possibility is that there are other undiscovered
mechanisms and pathways. Another possibility is that the acous-
tic level is higher than we measured, because we measured on a
quieter day. We do not know, because we do not have the physical
parameters. Bruce Walker suggests that sufficiently high levels
exist at some wind farms. Hessler’s relatively constant measured
data suggests we are not at a low power. So it seems this is another
conundrum, but again this is a needless problem that the power
company could sort out.
Analysis and Hypothesis Development
Point 1: Suggests looking for something in the 40-50 Hz range
as our possible “culprit.”
Point 2: Suggests that the electric power being generated is
a very important parameter to a person’s response. As Table 1
shows, the acoustic output is more or less constant over a wide
range of wind speeds, but the electrical power being generated is
changing with wind speed. It is true that the subjects in Cooper’s
study could have known when the sound, hence the wind farms,
were turning on and off, but they would have no way of knowing
the electric power from the acoustical signal. This lends strong
support to Cooper’s results.
Point 3: Suggests that there is a source of low-frequency audible
sound that is produced each time a blade passes the support tower
(or the low point of each blade during each revolution). The wind
turbine blades flex so that the blade tips come closer to the sup-
port tower (the flex increases) as the electric power being gener-
ated increases. The reverse occurs as the power being generated
decreases; the flex decreases and the minimum distance between
the support pole and the blade tip increases. So, this particular
sound increases and decreases in step with changes in the electric
power being generated.
The physical mechanism that is at work here is the same as a
stick or pole placed in a river. The pole represents an object that
can disrupt the regular flow. There is a big wake downstream as
everybody knows, but if one examines the situation a little
more closely, you realize that there has to be pressure reflected
upstream off this pole in the river, and that causes some distur-
bance upstream. The closer one is to the pole, the stronger the
upstream reflection effect is. Much the same is happening with
the wind turbine. As the blade gets closer to the support tower,
it gets into more of this upstream disturbance.
In summary, there is a sound source that produces low-frequency
pulses at the blade passage frequency, and the sound level of
the source goes up and down in accordance with the amount of
el ectri c power being generated. The facts in this analysis indicate
that this should be studied further, since this may be an important
factor in the community response – both annoyance and other
physiological effects. Moreover, the fact that this sound source can
be controlled by the operator, to some degree, gives some promise
to our ability to mitigate or eliminate this problem.
The hypothesis is that there is a frequency that will be char-
acteristic of a specific blade and manufacturer that based on the
discussion at ASA appears to be in the 25-60 Hz range. This tone
modulated at 1 Hz causes a reaction in at least some people. This
potential phenomenon should be able to be tested in a variety
of ways, most of them quickly and inexpensively.
Suggested Test 1
Diary Test. Using a diary study, one could ask respondents to
keep the following information:
• When they are at home and awake.
• The times when they feel a sensation caused by the wind tur-
bines.
Figure 4. Unacceptability ratings for group of “specials” to noise stimuli.
Unacceptability, %
100
50
020 - 30 30 - 40 40 - 50 50 - 60 60 - 70 70 - 80 80 - 90
Hertz
Annoyance specials N = 21
55 dB 65 dB 75 dB
Table 1. Electric power (kW) and acoustic A-weighted power level (dB) both
as functions of WS (m/s).
Wind Speed, Electricity Percent of Acoustical Power
10 m m/s Generated, kW Full Power Level, A-weighted dB
3* 34 1 95.5
4 88 4 100.5
5 237 9 103.0
6 448 18 106.5
7 738 30 107.5
8 1123 45 107.5
9 1604 64 107.5
10 2043 82 107.5
11 2321 93 107.5
12 2467 99 107.5
13 2500 100 107.5
14 2500 100 107.5
* 3.5 m/s for electric power; 3.0 m/s for acoustic power.
www.SandV.com 50th ANNIVERSARY ISSUE 39
• If so, how strong is the sensation?
This information could be related with electric power generated
and other physical parameters.
Suggested Test 2
Response Comparison. There are certainly some data that can
be examined that were gathered in conjunction with peoples’ re-
sponses. Hopefully, the Cooper data will show if specific tones in
this region are present, how strong they are, and how they compare
with the peoples’ responses.
General Tests
The two following tests are more general and would aid in un-
derstanding the phenomenon we are dealing with.
• Direct Human Testing. Direct human testing could be done in
laboratory and field settings but, as has been testified to, there
may be a period of time for the symptoms to incubate. A good
start on this is underway at the University of Minnesota.
• Direct Animal Testing. A cat or guinea pig’s ear could be used
to test for reaction to wind turbine noise. Monitoring could be
done on the nerve that emanates from the otolith and from the
nerves emanating from the cochlea as a function of wind turbine
sound amplitude both above and below the threshold of hearing.
Opinions and Recommendations of Bruce Walker
Modern large wind turbines produce pressure fluctuations as
the result of a variety of mechanisms. The time scales of these
fluctuations range from minutes to milliseconds (conversely the
frequency scales range from millihertz to kilohertz). Two aspects
of wind turbine noise that have received significant attention over
the past decade are amplitude-modulated broadband noise and
quasi-periodic “thumps” generated by interaction between rotor
blades and support towers. The focus of this review is the latter,
which is most commonly identified as wind turbine infrasound
(WTIS). In modern turbines, the time scale of this disturbance
is on the order 1 second. However, the details of the individual
disturbance events appear to hold the key to whether or not WTIS
results in human response.
Modeling
There has been a temptation to model WTIS using the same
techniques as for modeling audible sound: summation of spectral
sound pressure squared from multiple point sources. At Wind Tur-
bine Noise 2011,5 the modeling issue was addressed by observation
that the waveforms of WTIS were likely to be deterministic and
therefore add coherently, so that the more correct modeling would
be summation of time-domain sound pressures and subsequent
computation of peak and average sound pressure levels.
For multiple turbine installations, this would produce a wide
range of potential outcomes, depending on the relative synchro-
nization of the turbines. Figure 5 shows a hypothetical result for
five turbines turning at random speeds over a narrow range. For a
few minutes over a six-hour simulation period, peak levels over
10 dB above the SPL predicted from pressure-squared summing
were encountered. Receptors exposed to this momentary period of
enhanced pulsation levels could be highly annoyed or awakened
by it, while enforcement personnel might measure for hours and
never witness it.
Measurement
There has been a temptation to measure WTIS using the same
techniques as for measuring audible sound: time-averaged weighted
levels and power spectra. Typical field measurement results are
similar to those shown in Figure 6 acquired a few hundred meters
from a 2-3 MW range turbine. Spectral peaks are seen at several
multiples of the 0.75-Hz blade-passing frequency. The sound pres-
sure levels at each of these peaks is far below the generally accepted
sensation threshold.
However, the putative blade/tower interaction genesis of the
WTIS would suggest that the actual acoustic signal would be a
sequence of relatively narrow pulses. Further, the unsteadiness of
rotation speed would cause higher harmonic content of the signal
to migrate among conventional PSD analysis bins and appear as
broadband noise.
Figure 5. (a) Computed variations in SPL from a five-turbine array with
unequal rotation rates relative to incoherent result; (b) expansion of larg-
est peak.
Figure 6. Example of field measurement data.
www.SandV.com40 SOUND & VIBRATION/JANUARY 2017
Synthesis
An electro-acoustic system
was assembled starting in 2012
to synthesize periodic signals
with fundamental frequency
0.8 Hz and up to 65 harmonics
in a residential bedroom. A
photo of the system is shown
in Figure 10, and a schematic
of the test facility is shown
in Figure 11. Three 18-inch
“woofers” are driven by a DC-
coupled, 300-watt amplifier,
excited by Fourier-synthesized
waves from 16-bit, D-to-A converters. A second loudspeaker can
provide synchronized amplitude-modulated, Dopplerized, audible
sound if desired. An infrasound microphone is suspended above
the evaluator’s head. The system was described in detail at Wind
Turbine Noise, 2015.9
Spectra corresponding to variations on that shown in Figure 12
were presented to a variety of volunteers at levels extending to ap-
proximately 15 dB above those reported from field measurements.
Harmonic phases were adjusted to maximize or minimize signal
crest factor and signal peak slope. If the upper limit of spectral
content was 20 Hz or below, no evaluator reported any sensation.
With the upper limit extended to 32 Hz and the level above 20 Hz
spectrally uniform, one evaluator reported significant unease after
a few minutes exposure. Subsequently, this evaluator reported
unease when exposed only to amplitude-modulated audible sound.
In 2014, Hansen et al.,10 obtained field measurement data that
displayed periodic spectral detail that extended to above 50 Hz, as
shown in Figure 13. At ASA 2014 and Wind Turbine Noise 2015,
Palmer11 showed correlations of resident response to nearby opera-
tions of turbines that depended on resident positions inside rooms.
This suggested the possibility that the residents were affected by
sound of frequency high enough to excite room resonances, typi-
cally 30-40 Hz and above.
The Hansen data were analyzed extensively and results pre-
sented in Wind Turbine Noise 2015.12 All spectral lines were
separated by the turbine BPF, but in some ranges, the actual
frequencies were not exact multiples of BPF. The mechanism for
generating such a spectrum could be brief bursts of mechanical
resonance once per blade pass or the effect of multiple turbines at
slightly different speeds. The spectra were forced into a harmonic
series and synthesized for evaluation. Because the reported power
spectra lacked phase information, all harmonics were assumed to
be at zero phase simultaneously.
Response
Threshold, annoyance and sleep interference were informally
investigated using the full Hansen spectrum, then with high-pass
filtering at 20 and 30 Hz and finally with low-pass filtering at 20
Hz. In summary, high-pass filtering had no effect on any parameter,
and low-pass filtering resulted in no response, even with 10 dB
exaggerated levels.
The results of these informal tests were presented at Wind
Turbine Noise 2015, with admonition that they represent small
samples and relatively brief (10 minutes to 2 hours) exposure. It
was recommended that more extensive similar investigations be
undertaken.
Follow-Up
During Wind Turbine Noise 2015, and discussions with co-
authors, it appeared that the Hansen spectrum could be approxi-
mated by a uniform BPF harmonic series, weighted by a sin(pf/18)/
(pf/18) shape function.
The resulting waves and spectra are shown in Figures 14-16.
Figure 16 demonstrates that once each blade-pass period, the sig-
nal harmonics from the third spectrum lobe may constructively
combine, producing a periodic “thud” that at levels just slightly
above hearing threshold, produces an illusion of infrasound that
is devoid of actual infrasonic energy. Note that near 45 Hz, the
At Low Frequency Noise 2012,6 Wind Turbine Noise 20137
and ASA 2014,8 methods were described for capturing the wave
form emitted by large wind turbines by synchronous sampling
and ensemble averaging several-minute recorded samples from a
three- and four-microphone array. These measurements confirmed
that the emitted infrasound was confined to less than 10% of the
blade-pass period, as shown in Figure 7. One set of measurements
suggested that the phase of the BPF signal component depended
on azimuth, as shown in Figure 8. The algorithms used to simulate
synchronous sampling left too much residual jitter to retain time
resolution better than approximately 50 ms.
Figure 7. Example ensemble average waveform and time derivative with
wind direction 140° re mic orientation.
Figure 8. Example ensemble average waveform and time derivative with
wind direction 60° re mic orientation.
Figure 9. Shaft-order spectrum for wave shown in Figure 8.
Figure 10. Loudspeakers for WTIS
synthesis in 43 m3 test room.
www.SandV.com 50th ANNIVERSARY ISSUE 41
maximum SPL is 13 dB above Leq, so a measured spectral “hump”
that appeared to be well below threshold could easily produce
audible “thumps” that would be mistaken for infrasound. The time
between the negative and positive peaks in the full-spectrum wave
is 0.055 seconds, in which time the rotor blade tip would travel
4.6 meters at 84 mps tip speed. This seems reasonable for the ap-
proximate width of the support tower or its bow wake, supporting
blade/tower interaction as a genesis mechanism.
An observation from the idealized spectrum shown in Figure
14 is that the phases of the components in the second lobe would
be reversed relative to the first and third lobes. This detail was
not followed in perception testing. In Figure 15, the effect of the
phase reversal on the composite waveform is displayed. The crest
factor and wave “sharpness” are clearly increased with the second
lobe phase properly reversed. When reproduced at 10× frequency
Figure 11. Layout of WTIS evaluation test room.
Figure 12. Generic WTIS spectrum used for initial evaluations.
Figure 13. Outdoor (a) and indoor (b) spectra of WTN measured by Hansen.
on loudspeakers, the properly phase-reversed signal is distinctly
more impulsive sounding. The effect on perception at full-scale
frequency is currently being explored.
Summary and Collective Recommendations
Disclaimer. The preceding sections are the sole and exclusive
work of each author. There has been no attempt at editing or reach-
ing agreement among authors.
Areas Identified for Needed Practical Research
Simulation. Walker has demonstrated that wind turbine infra-
Figure 14. Spectrum of sin(x)/x-weighted BPF harmonics.
www.SandV.com42 SOUND & VIBRATION/JANUARY 2017
Figure 15. Waveform of spectrum shown in Figure 14.
Figure 16. Wave-packet representation of third-spectrum lobe components.
Figure 17. Typical spectrum from a large, modern, , 3-MW wind turbine.
Figure 18. Calculated Lp spectra as function of distance.
sound and pulsed LFN, which may be upper harmonics of the
Infrasound pulsations, can be mathematically defined, duplicated
and simulated with loudspeakers for subject evaluator testing. A
more formal and expanded set-up, perhaps at a university using
student volunteers exposed to both low and high levels could es-
tablish the threshold of perception for both steady and pulsed LFN
for the particular and unique source of environmental noise from
wind turbines. Studies in this area are progressing in Australia.
Survey of Wind Turbine Projects Participating Residents. Land-
owners who lease their land for wind turbine installations may ex-
perience sound levels well in excess of proposed limits for normal
siting practices and experience higher levels than nonparticipating
neighbors. There should be an absolute wealth of information to be
learned from these residents collected by a well-designed national
survey. Such a survey must have the complete cooperation and
possible sponsorship from the industries’ national representative,
AWEA (American Wind Energy Association) in America and others
throughout the world. The authors would like to suggest questions
to any study team.
Noise Source Reduction. The designers and suppliers of wind
turbines must make a continued and concerted effort to reduce
noise emissions from their turbine designs. Reductions can be
accomplished by a combination of blade design and operational
software. A universal design goal based on measurable established
standards (IEC-61400) for sound power level would encourage
these efforts.
Perception Testing. Schomer suggests pathways that could sup-
port some test findings in America and Australia that suggest from
statistical correlation that some residents could perceive wind
turbine operation and/or operational changes without benefit of
sight or audibility. A detailed discussion is offered on practical
perception testing that could discover something unknown to
us at this time and is highly recommended for implementation.
Discussion and Collective Conclusion
None of these opinions and recommendations answers the posed
question: does ILFN from wind turbines make people sick? It is
abundantly obvious that intense adverse response occurs at cer-
tain sites. Realistically, it is not even possible to answer the posed
question to all parties’ satisfaction with practical research. For
examples, a direct link to adverse health effects from yesterday’s
tobacco and today’s excess sugar can be denied forever, because any
research that could actually prove a link to all parties would take
longer than forever and would be totally impractical. The wind
farm industry must accept that there are enough worldwide sites
that emit excessive wind turbine noise resulting in severe adverse
community response to adopt and adhere to a reasonable sound
level limit policy. Likewise, wind farm opponents must accept
reasonable sound limits or buffer distance to the nearest turbine –
not pie-in-the-sky limits to destroy the industry.
The A-weighted sound level is commonly used for assessing
noise from wind farms as well as most all other large power genera-
www.SandV.com 50th ANNIVERSARY ISSUE 43
Table 2. Maximum allowable C-weighted sound level, LCeq, at residential
areas to minimize infrasound noise and vibration problems.
Normal Suburban/Urban Very Quiet Suburban or
Residential Areas, Rural Residential Areas,
Daytime Residual Level, Daytime Residual Level,
L90 > 40 dBA L90 > 40 dBA
Intermittent day-only 70 66
or seasonal source
operation
Extensive or 24 / 7 65 60
source operation
Figure 19. Overall levels as function of distance.
tion facilities. Each author has been recommending the following
limits for wind farm noise emissions for years: Hessler13 – 40 dBA
design goal, 45 dBA max limit; Leventhall – 40 dBA; Schomer –
35-39 dBA; and Walker – 45 dBA in high ambient areas but lower
in lower area ambient locales. The authors have generally found
that wind farms designed to a level of 40 dBA or a bit lower at
nonparticipating residential receptors have an acceptable com-
munity response. Surveys at wind farm sites for a decade have
consistently shown good statistical correlation between wind
farm noise level emissions and the percentage of highly annoyed
residential receptors (% HA).
The question arises if an A-weighted criterion alone is adequate
to protect receptors from infrasound (IS), LFN and pulsed LFN
shown to be present in large wind turbines. Figure 17 plots the mea-
sured spectrum from a typical, nominal, 3-MW wind turbine plus
the most commonly used overall levels. Infrasound (IS), the highest
overall level, is calculated by summing the bands 1-16 Hz (0.7-22
Hz) and LFN by summing the bands 31.5-125 Hz for a frequency
band of 22-177 Hz. Note that the overall C-weighted level and LFN
levels are quite close together. Notice also that C-weighting filters
out IS and would not be a good metric for assessing wind turbine
IS but would be excellent for assessing LFN from wind turbines.
Hessler14 and Broner15 have recommended C-weighting limits
for low-frequency industrial sources based principally on extensive
experience with open-cycle combustion turbines. Both have con-
cluded independently that a level of 60 dBC is a desirable criterion
to minimize adverse response from neighboring communities as
shown in Table 214 and Table 3.15 the C-weighted level from wind
turbines will always be comfortably below 60 dBC when emitting
40 dBA or less.
Figure 18 illustrates the computed pressure spectra from 250 m
(820 feet) to 64,000 m (40 miles). The calculation uses ISO-9613
algorithms for hemispherical divergence, air absorption and ground
effects assuming a 100-m hub height. Note that 3 dB/doubling
distance in lieu of 6 dB is used for IS beyond 1 km as measured in
the recent extensive Health Canada study. The reason for doing
this calculation is to determine the overall levels with distance
that is shown in Figure 19.
Looking at the octave-band spectra, it is apparent that the indica-
tor of a potential low-frequency noise problem, C-A level, should
increase with distance, since the A-weighting level is reduced by
excess attenuation while low frequency noise is not. The result
is 11 increasing to 24 dB if the ambient is not considered in the
calculation. However, when a macro residual ambient of 25 dBA
is assumed, the quantity starts at 11 dB and actually decreases to
zero, as shown on Figure 19. This classic indicator of a potential
low-frequency problem when C-A reaches 15 to 20 dBC will not
occur when assessing LFN at wind turbine sites.
Collective Conclusions
Our analysis illustrates that a wind turbine is not a classic LFN
source; that is, one with excessive low-frequency spectral content.
But a wind turbine is a unique power-generating source with spec-
tral content down to the 1-Hz octave band, emitting measurable IS
in addition to LFN. Infrasound (IS, 0-20 Hz) from wind turbines
can almost be ruled out as a potential mechanism for stimulating
motion sickness symptoms. But to be thorough and complete, we
recommend that one or two relatively simple and relatively inex-
pensive studies be conducted to be sure no infrasound pathways to
the brain exist other than through the cochlea. Pending the results
of these studies, we feel that no other IS or LFN criteria are required
beyond an acceptable A-weighted level.
References
1. What You Need to Know About Seasickness or Motion Sickness, Cleve-
land Clinic, http://my.cleveland clinic.org/
2. Graphic, Noise and Health, Bimonthly Interdisciplinary Journal, June
2004.
3. “A Cooperative Measurement Survey and Analysis of Low Frequency
and Infrasound at the Shirley Wind Farm in Brown County, Wisconsin,”
Report Number 122412-1, Appendix B, PSC REF#: 178263, Dec 24, 2012.
4. Project EARS, “Assessment and Safety of Non- Audible Sound,” Table
2, Communique 2015.
5. Walker, B. “Coherence Issues in Wind Turbine Noise Assessment,”
Fourth International Meeting on Wind Turbine Noise, Rome, Italy, April
2011.
6. Walker, B. “Time Domain Analysis of Low-Frequency Wind Turbine
Noise,” 15th International Meeting on Low Frequency Noise and its
Control, Stratford Upon Avon, UK, May 2012.
7. Walker, B. “Infrasound Measurement, Interpretation and Misinterpreta-
tion,” 5th International Meeting on Wind Turbine Noise, Denver, CO,
August 2013.
8. Walker, B., Celano, J., “Measurement and Synthesis of Wind Turbine
Infrasound,” ASA Indianapolis, IN, 2014.
9. Walker, B., Celano J., “Progress Report on Synthesis of Wind Turbine
Noise and Infrasound,” 6th International Meeting on Wind Turbine
Noise, Glasgow, Scotland, April 2015.
10. Hansen, K., Zajamsek, B, Hansen, C. “Identification of Low Frequency
Wind Turbine Noise Using Secondary Wind Screens of Various Geom-
etries,” NCEJ 62(2), March-April 2014.
11. Palmer, W. “Wind Turbine Annoyance – A Clue from Acoustic Room
Modes,” JASA 136, 2204, 2014.
12. Hansen, K., Walker, B., Zajamsek, B., Hansen, C., “Perception and An-
noyance of Low Frequency Noise Versus Infrasound in the Context of
Wind Turbine Noise,” 6th International Meeting on Wind Turbine Noise,
Table 3. Criteria for assessment of LFN.
Sensitive Receiver / Operation Range Critera Leq, dBC
Residential Nighttime / plant ops. Desirable 60
24 /7 Maximum 65
Daytime / intermittent Desirable 65
1 - 2 hours Maximum 70
Commercial / Nighttime or plant ops. Desirable 70
office 24 / 7 Maximum 75
Industrial Daytime or intermittent Desirable 75
1 - 2 hours Maximum 80
www.SandV.com44 SOUND & VIBRATION/JANUARY 2017
Glasgow, Scotland, April 2015.
13. Hessler, G.F., Hessler, D.M., “Recommended Noise Level Design Goals
and Limits at Residential Receptors for Wind Turbine Developments in
the United States,” Noise Control Engineering Journal, 59(1), Jan-Feb
2011.
14. Hessler, G.F., “Proposed Criteria in Residential Communities for Low-
frequency Noise Emissions from Industrial Sources,” Noise Control
Engineering Journal, 52 (4), , Jul-Aug 2004.
15. Broner, N., “A Simple Criterion for Assessing Low Noise Emissions,”
Journal of Low Frequency Noise, Vibration and Active Noise Control,
UK ISSN 0263, Volume 29, Number 1, 2010.
Ashmore, J., et al. (2010). “The Remarkable Cochlear Amplifier.” Hearing
Research 266: 1-17.
Benton, S. and H. G. Leventhall (1994). “The Role of ‘Background Stressors’
in the Formation of Annoyance and Stress Responses.” Jnl Low Freq Noise
Vibn 13(3): 95-102.
Bray, W. and R. James (2011), “Dynamic Measurements of Wind Turbine
Acoustic Signals,” Proc. Noise-Con, 2011.
Chapman, S., et al. (2014), “Fomenting Sickness: Nocebo Priming of Resi-
dents About Expected Wind Turbine Health Harms,” Frontiers in Public
Health: doi: 10.3389/fpubh.2014.00279.
Crichton, F., et al. (2014), “Can Expectations Produce Symptoms from
Infrasound Associated with Wind Turbines?” Health Psychology, 33(4):
360-364.
Deignan, B., et al. (2013), “Fright Factors About Wind Turbines and Health
in Ontario Newspapers Before and After the Green Energy Act,” Health,
Risk and Society: 234-250, http://dx.doi.org/210.1080/13698575.13692
013.13776015.
Dobie, R. (2014), “Letter to the Editor,” Acoustics Today, 10(2): 14.
Henkel, L.A., M.E. Mattson (2011), “Reading is Believing: The Truth Effect
and Source Credibility,” Consciousness and Cognition, 20(4): 1705-1721.
Jalali, L., et al. (2016), “The Impact of Psychological Factors on Self-Reported
Sleep Disturbance Among People Living in the Vicinity of Wind Turbines,”
Environmental Research, 148 401-410.
Job, R.F.S. (1988), “Community Response to Noise: A Review of Factors
Influencing The Relationship Between Noise Exposure and Reaction,” J.
Acoust. Soc. Am., 83 (3), : 991 - 1001.
Keith, S.E., et al. (2016), Wind Turbine Sound Power Measurements,” J.
Acoust. Soc. Am., 139(3): 1431-1435.
Kuehler, R., et al. (2015), “Infrasonic and Low-Frequency Insert Earphone
Hearing Threshold,” J. Acoust. Soc. Am., Express Letters, 4(137): EL347.
Landström, U., et al. (1983), “Exposure to Infrasound – Perception and
Changes in Wakefulness,” Jnl. Low Freq Noise Vibn, 2(1): 1-11.
Leventhall, G. (2013a), “Concerns About Infrasound from Wind Turbines,”
Acoustics Today, 9(3): 30-38.
The authors can be reached at the following: george@hesslerassociates.com;
geoff@activenoise.co.uk; schomer@schomerandassociates.com; noiseybw@
aol.com.
Leventhall , G., et al. (2012) “Helping Sufferers to Cope With Noise Using
Distance Learning Cognitive Behaviour Therapy,” J. Low Frequency Noise,
Vibration and Active Control, 31(3): 193-204.
Leventhall, H. G. (1998), “Making Noise Comfortable for People,” ASHRAE
Transactions, Vol. 104, pt1,: 896 - 900.
Michaud, D.S., et al. (2016), “Effects of Wind Turbine Noise on Self-Reported
and Objective Measures of Sleep,” Sleep, 39(1): 97-109.
Mroczek , B., et al. (2015). “Evaluation of Quality of Life of Those Living
Near a Wind Farm.” Int. J. Environ. Res. Public Health doi:10.3390/
ijerph120606066(12): 6066-6083.
Nissenbaum, M.A., et al. (2012), “Effects of Industrial Wind Turbine Noise
on Sleep and Health,” Noise and Health, 14: 237-243.
Rainford, D., Gradwell, D.P., Ernsting, J., (2006), “Enrsting’s Aviation Medi-
cine,” 4th Edition. London: Hodder Arnold.
Rubin, G.J., et al. (2014),”Possible Psychological Mechanisms for ‘Wind
Turbine Syndrome’ on the Windmills of Your Mind,” Noise and Health,
16(69): 116-122.
Salt, A.N., Hullar, T.E., (2010), “Responses of the Ear to Low Frequency
Sounds, Infrasound and Wind Turbines,” Hearing Research, 268 12-21.
Salt, A. N. , Lichtenhan, J.T., (2014), “How Does Wind Turbine Noise Affect
People?” Acoustics Today. 10(1): 20-28.
Schomer, P. (2015), “A proposed test of some people’s ability to sense wind
turbines without hearing or seeing them,” Proc. of Meetings on Acous.,
25(1): 1-5.
Shams, Q.A., et al. (2013), “Experimental Investigation into Infrasonic
Emissions from Atmospheric Turbulence,” J. Acoust. Soc. Am., 133(3):
1269-1280.
Tachibana, H., et al. (2014), “Nationwide Field Measurements of Wind
Turbine Noise in Japan,” Noise Control Eng Jnl, 62( 2): 90-101.
Tonin, R., et al. (2016). “The Effect of Infrasound and Negative Expectations
to Adverse Pathological Symptoms from Wind Farms,” Jnl Low Freq Noise
Vibn Ac Cntrl, 35(1): 77-90.
Turnbull, C., et al (2012), “Measurement and Level of Infrasound from Wind
Farms and Other Sources,” Acoustics Australia, 40(1): 45-50.
Witthoft, M., Rubin, J.G., (2013), “ArevMedia Warnings About the Adverse
Health Effects of Modern Life Self-Fulfilling?” An experimental study on
idiopathic environmental intolerance attributed to electromagnetic fields
(IEI-EMF), Jnl Psychosomatic Research, 74: 206-212.
Zajamšek, B., et al. (2016), “Characterisation of Wind Farm Infrasound And
Low-Frequency Noise,” Jnl Sound Vibration, 370: 176–190.