The Wind of Change: When You Hear a Sound

Scorpions’ ‘Wind of Change’: The Oral History of 1990’s Epic Power Ballad
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Calvert, Sept. My apologies for that calculation error. Best regards, Omnivorous-GA. But after I posted the first Clarification Request, I realized that I'd done the math backwards in the sound calculations. The third paragraph should be replaced by the following: "Sound will arrive downwind 0. There is less absorption of the sound wave because the wave has traveled less distance and had energy absorbed by fewer air molecules?

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Seriously, there are a lot of good sources here, and that is important. You can pretty much find a site that will say anything on the Internet today, so credible sources is key to any answer. The response was well thought out and well organized as well. From: racecar-ga on 01 Aug PDT.

If the sound meters are fixed relative to the source, the wind does not cause a shift if the frequency detected. From: omnivorous-ga on 01 Aug PDT. Racecar -- I don't believe that you are correct unless describing a no-wind situation.

Etude 1: Wind Tones

From: iang-ga on 02 Aug PDT. The Doppler calculation assumes the observer is stationary with respect to the medium. In this case they're both moving with respect to the medium but they're stationary with respect to each other - there's no effect on the wavelength. Ian G. From: racecar-ga on 02 Aug PDT.

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Respectfully, the comments by both omnivourous and iang are incorrect. When source and observer are not moving relative to each other, but both are moving relative to the medium, there IS an effect on the wavelength, but none on the frequency. As omnivorous says, the sound travels slower relative to the ground upwind than downwind, but the wavelength also shortens, and the frequency doesn't change. Think about it this way: frequency is the number of wave crests that arrive in say a second.

Let's say the frequency is hertz. That means every second waves leave the source. Now the receiver is a certain distance away. If fewer or more than waves arrive at the receiver every second where do those extra waves go? In the case where source and receiver are moving relative to each other, the extra waves go to fill up the changing distance between the source and receiver.

But in this case, the distance between source and receiver doesn't change, so the number of wave crests between them doesn't change, and there can be no shift in frequency. Omnivorous, if this doesn't make sense to you, I'm sure I can dig up some online references. Important Disclaimer: Answers and comments provided on Google Answers are general information, and are not intended to substitute for informed professional medical, psychiatric, psychological, tax, legal, investment, accounting, or other professional advice.

The British Wind Energy Association , states that sounds from wind turbines are in the 30—50 dBA range, a level they correctly describe as difficult to discern above the rustling of trees [i. This begs the question of why there is such an enormous discrepancy between subjective reactions to wind turbines and the measured sound levels. Many people live without problems near noisy intersections, airports and factories where sound levels are higher.

The answer may lie in the high infrasound component of the sound generated by wind turbines. A detailed review of the effects of low frequency noise on the body was provided by Leventhall This review considers the factors that influence how different components of the ear respond to low frequency stimulation and specifically whether different sensory cell types of the inner ear could be stimulated by infrasound at the levels typically experienced in the vicinity of wind turbines. Sounds represent fluctuating pressure changes superimposed on the normal ambient pressure, and can be defined by their spectral frequency components.

Sounds with frequencies ranging from 20 Hz to 20 kHz represent those typically heard by humans and are designated as falling within the audible range. Sounds with frequencies below the audible range are termed infrasound. The boundary between the two is arbitrary and there is no physical distinction between infrasound and sounds in the audible range other than their frequency. Indeed, infrasound becomes perceptible if presented at high enough level.

The level of a sound is normally defined in terms of the magnitude of the pressure changes it represents, which can be measured and which does not depend on the frequency of the sound. In contrast, for sounds of constant pressure, the displacement of the medium is inversely proportional to frequency, with displacements increasing as frequency is reduced. This phenomenon can be observed as the difference in vibration amplitude between a subwoofer generating a low frequency tone and a tweeter generating a high frequency tone at the same pressure level.

The speaker cone of the subwoofer is visibly displaced while the displacement of the tweeter cone is imperceptible. As a result of this phenomenon, vibration amplitudes to infrasound are larger than those to sounds in the auditory range at the same level, with displacements at 1 Hz being times those at 1 kHz when presented at the same pressure level. The auditory part of the inner ear, the cochlea, consists of a series of fluid-filled tubes, spiraling around the auditory nerve.

A section through the middle of a human cochlea is shown in Fig 1A. The anatomy of each turn is characterized by three fluid-filled spaces Fig 1B : scala tympani ST and scala vestibuli SV containing perilymph yellow , separated by the endolymphatic space ELS blue. The two perilymphatic compartments are connected together at the apex of the cochlea through an opening called the helicotrema. The organ of Corti, seen here in cross section, contains one row of inner hair cells IHC and three rows of outer hair cells OHC along the spiral length of the cochlea.

As shown schematically in Fig 1F , the sensory hairs stereocilia of the OHC have a gradation in length, with the tallest stereocilia embedded in the gelatinous tectorial membrane TeM which overlies the organ of Corti in the endolymphatic space Kimura This arrangement allows sound-evoked displacements of the organ of Corti to be converted to a lateral displacement of OHC stereocilia. In contrast, the stereocilia of the IHC do not contact the tectorial membrane, but remain within the fluid of the subtectorial space Kimura , Lim Because of this difference in how the hair cell stereocilia interact with the TeM, the two types of hair cell respond differently to mechanical stimuli.

At low frequencies, the IHC respond according to the velocity of basilar membrane displacement, while OHC respond to the displacement itself Russell and Sellick, ; Dallos, Panels A—E Cross section through the human cochlea shown with progressively increasing magnification. Panels B and C The fluid spaces containing perilymph have been colored yellow and endolymph blue. Panel D The sensory structure of the cochlea, the organ of Corti, is colored green.

Panel F Schematic showing the anatomy of the main components of the organ of Corti. The two types of hair cells also contact different types of afferent nerve fibers, sending information to the brain Spoendlin, ; Santi and Tsuprun, Type II afferents fibers are believed to be unresponsive to sounds and may signal the static position of the organ of Corti Brown, ; Robertson et al. The OHC also receive substantial efferent innervation from the brain while the IHC receive no direct efferent innervation Spoendlin, Infrasound entering the ear through the ossicular chain is likely to have a greater effect on the structures of the inner ear than is sound generated internally.

The basic principles underlying stimulation of the inner ear by low frequency sounds are illustrated in Figure 2. Panel A shows the compartments of a simplified, uncoiled cochlea bounded by solid walls with two parallel fluid spaces representing SV and ST respectively that are separated by a distensible membrane representing the basilar membrane and organ of Corti.

In example A, all the boundaries of the inner ear are solid and noncompliant with the exception of the stapes. In this non-physiologic situation, the stapes applies pressures to SV indicated by the red arrows but as the fluid can be considered incompressible, pressures are instantaneously distributed throughout both fluid spaces and pressure gradients across the basilar membrane will be small.

For frequencies below Hz the RW provides a compliance between perilymph and the middle ear Nakajima et al. Under this condition, pressures applied by the stapes induce small volume flows between the stapes and the site s of compliance blue arrows which requires a pressure gradient to exist along the system, as indicated by the shading. This is the situation for external sounds entering the normal cochlea via the ossicular chain. In this case, the compliant RW is situated close to the location of aqueduct entry, so the major fluid flows and pressure gradients occur locally between these structures.

As the stapes and other boundaries in scala vestibuli and the vestibule are relatively noncompliant, pressure gradients across the basilar membrane will be lower than with an equivalent pressure applied by the stapes. For infrasonic frequencies, it was shown that responses to 1 Hz pressure oscillation applied to the fluid in the basal turn of ST were substantially increased when the wall of SV was perforated thereby providing greater compliance in that scala Salt and DeMott, Schematic representation of the uncoiled inner ear for four different mechanical conditions with low frequency stimulation.

Red arrows indicate applied pressure and blue arrows indicate loss to compliant structures. Sound pressure applied by the stapes causes uniform pressures indicated by color shading throughout the fluid space, so pressure difference across the basilar membrane and therefore stimulation is minimal. B: The normal situation with compliances provided by the round window and cochlear aqueduct at the base of scala tympani. Pressure differentials cause movement of fluid towards the compliant regions, a including a pressure differential across the basilar membrane causing stimulation.

C: Situation where low frequency enters scala tympani through the cochlear aqueduct. The main compliant structure is located nearby so pressure gradients across the basilar membrane are small, limiting the amount of stimulation. Infrasound entering through the cochlear aqueduct such as from respiration and body movements therefore does not provide the same degree of stimulation as that entering via the stapes. D: Situation with compromised otic capsule, such as superior canal dehiscence. As pressure gradients occur both along the cochlea and through the vestibule and semi-circular canal, the sensory structures in the semi-circular canal will be stimulated.

The endolymphatic duct and sac is not an open pathway but is closed by the tissues of the sac, so it is not considered a significant compliance. It may also produce an abnormal sound-induced stimulation of other receptors in the inner ear, such as the hair cells in the ampulla of the semicircular canal. This is the basis of the Tullio phenomenon, in which externally or internally generated sounds, such as voice, induce dizziness.

Receptors in other organs of the inner ear, specifically both the saccule and the utricle also respond to airborne sounds delivered by the stapes, as discussed in more detail below. The mechanism of hair cell stimulation of these organs is less certain, but is believed to be related to pressure gradients through the sensory epithelium Sohmer When airborne sounds enter the ear, to be transduced into an electrical signal by the cochlear hair cells, they are subjected to a number of mechanical and physiologic transformations, some of which vary systematically with frequency.

The main processes involved were established in many studies and were summarized by Cheatham and Dallos A summary of the components are shown in Figure 3. There are three major processes influencing the sensitivity of the ear to low frequencies. A second process attenuating low frequency sounds is the fluid shunting between ST and SV through the helicotrema.

The third filter arises from the demonstrated dependence of the IHC on stimulus velocity, rather than displacement Dallos, The combined results of these processes are compared with the measured sensitivity of human hearing ISO in Fig 3B. This steep cutoff means that to hear a stimulus at 5 Hz it must be presented at dB higher level than one at Hz. However, an important consequence of this underlying mechanism is that the OHC and IHC differ markedly in their responses to low frequency stimuli.

In theory, the difference between IHC and OHC responses will increase as frequency decreases becoming over 50 dB at 1 Hz , but in practice, there is interaction between the two types of hair cells which limits the difference as discussed below. Upper panel: Estimated properties of high pass filter functions associated with cochlear signal processing based on Cheatham and Dallos, Lower panel: Combination of the three processes above into threshold curves demonstrating: input to the cochlea dotted as a result of middle ear attenuation; input to the outer hair cells OHC as a result of additional filtering by the helicotrema; and input to the IHC as a result of their velocity dependence.

The cochlear microphonics CM recorded in the organ of Corti with low frequency stimuli are in phase with the intracellular potentials of the OHC. This supports the view that the low-frequency CM is dominated by OHC-generated potentials, which follow the displacement of the basilar membrane Dallos et al. As frequency is lowered, the intracellular potentials of IHC and afferent fiber responses show phase changes consistent with the IHC no longer responding to the increasingly attenuated velocity stimulus, but instead responding to the extracellular potentials generated by the OHC Sellick et al, , Cheatham and Dallos It can be inferred that if extracellular voltages generated by the OHC are large enough to electrically stimulate the IHC at a specific frequency and level, then the lowest level that the OHC respond to at that frequency must be substantially lower.

Based on this understanding of how the sensitivity of the ear arises, one conclusion is that at low frequencies the OHC are responding to infrasound at levels well below those that are heard. Although the OHC at 1 kHz are approximately 12 dB less sensitive than IHC Dallos , this difference declines as frequency is lowered and differences in hair cell sensitivity at very low frequencies below Hz have not been measured.

Much of the work understanding how the ear responds to low frequency sounds is based on measurements performed in animals. Although low frequency hearing sensitivity depends on many factors including the mechanical properties of the middle ear, low frequency hearing sensitivity has been shown to be correlated with cochlear length for many species with non-specialized cochleas, including humans and guinea pigs West, ; Echteler et al.

The thresholds of guinea pig hearing have been measured with stimulus frequencies as low as 50 Hz, as shown in Fig 4A. The average sensitivity at Hz for five groups in four studies Heffner et al. In the absence of data to the contrary, it is therefore reasonable to assume that if low frequency responses are present in the guinea pig at a specific level, then they will be present in the human at a similar or lower stimulus level.

Upper panel: Similar filter functions as Fig 3 , with parameters appropriate for the guinea pig, and compared with measures of guinea pig hearing. At Hz the guinea pig is approximately 18 dB less sensitive than the human shown dotted for comparison. Middle panel: Cochlear microphonic isopotential contours in the guinea pig show no steep cutoff below Hz, consistent with input to the OHC being maintained at lower levels than the IHC for low frequencies.

Also shown for comparison is the estimated input sensitivity for the OHC with the attenuation by the helicotrema excluded. CM sensitivity curves both have lower slopes than their predicted functions, but the change caused by helicotrema occlusion is comparable. The sensitivity of CM as frequency is varied is typically shown by CM isopotential contours, made by tracking a specified CM amplitude as frequency is varied. The decrease in CM sensitivity as frequency is lowered notably follows a far lower slope than that of human hearing over the comparable frequency range, In the data from Salt et al.

Although these are suprathreshold, extracellular responses, based on an arbitrary amplitude criterion, these findings are consistent with the OHC having a lower rate of cutoff with frequency than the IHC, and therefore responding to lower level stimuli at very low frequencies.

The measured change in CM sensitivity with frequency may include other components, such as a contribution from transducer adaptation at the level of the OHC stereocilia Kros, Kennedy et al. This type of adaptation, however, does not appear to provide additional attenuation at very low frequencies, as inferred from CM sensitivity curves measured down to 5 Hz. On the contrary, the CM sensitivity curve appears to flatten below 10 Hz, a phenomenon which is currently under investigation in our laboratory.

This contrasts with a prior suggestion that the helicotrema of the guinea pig was less effective than that of other species Dallos, The operating point can be regarded as the resting position of the organ of Corti or its position during zero crossings of an applied stimulus which may not be identical, as stimulation can itself influence operating point. Low frequency sounds so called bias tones have been shown to modulate distortion generated by the ear by their displacement of the operating point of the organ of Corti Brown et al. In normal guinea pigs, 4. This is a level that is substantially below the expected hearing threshold of the guinea pig at 4.

In animals where the helicotremea was occluded by injection of gel into the perilymphatic space at the cochlear apex, even lower bias levels down to 60 dB SPL modulate operating point measures Salt et al. A similar hypersensitivity to 4.

For the Contemporary Flutist

This was thought to be related to the occlusion of the helicotrema by the displaced membranous structures bounding the hydropic endolymphatic space in the apical turn. In the human ear, most studies have focused on the 2f 1 —f 2 distortion product, as even-order distortions are difficult to record in humans. The 2f 1 —f 2 component has been demonstrated to be less sensitive to operating point change Sirjani et al. Using different criteria of bias-induced distortion modulation, the dependence on bias frequency was systematically studied in humans for frequencies down to 25 Hz, 6 Hz and 15 Hz respectively Bian and Scherer, , Hensel et al, , Marquardt et al, In each of these studies, the bias levels required were above those that are heard by humans, but in all of them the change of sensitivity with frequency followed a substantially lower slope than the hearing sensitivity change as shown in Figure 5.

Again this may reflect the OHC origins of acoustic emissions, possibly combined with the processes responsible for the flattening of equal loudness contours for higher level stimuli, since the acoustic emissions methods are using probe stimuli considerably above threshold. It should also be emphasized that each of these studies selected a robust modulation criterion and was not specifically directed at establishing a threshold for the modulation response at each frequency. Indeed, in the data of Bian and Scherer their Figure 3 , significant modulation can be seen at levels down to 80 dB SPL at some of the test frequencies.

InSight Uses its Seismometer to "Hear" the Sound of Wind on Mars - Universe Today

In one of the studies Marquardt et al, equivalent measurements were performed in guinea pigs. Although somewhat lower slopes were observed in guinea pigs it is remarkable that stimulus levels required for modulation of distortion were within 5—10 dB of each other for guinea pigs and humans across most of the frequency range. In this case the guinea pig required lower levels than the human.

In the Marquardt study, the bias tone level required at Hz is over 60 dB above hearing threshold at that frequency. Frequency dependence of low frequency bias induced modulation of the 2f 1 —f 2 distortion product measured in the external ear canal of humans in three studies, compared with estimated input functions and human hearing sensitivity.

Below Hz the sensitivity to bias falls off at a much lower slope than human hearing, consistent with the response originating from OHC with a lower cutoff slope. The OHC not only transduce mechanical stimuli to electrical responses, but also respond mechanically to electrical stimulation reviewed by Dallos in a manner that provides mechanical amplification. For low frequency stimulation, however, basilar membrane modulation by the low frequency tone does have a major influence on the mechanics at the best frequency of high frequency tones i.

Patuzzi et al. It has been suggested that slow mechanical movements of the OHC may play a part in stabilizing the operating point of the transducer LePage ; LePage so the OHC may participate in an active cancellation of low frequency sounds. In models of the cochlear transducer, it was proposed that negative feedback occurred at low frequencies in which the OHC opposed movements of the basilar membrane , which becomes a positive feedback at the best frequency for the region Mountain et al. Chan and Hudspeth have also suggested OHC motility may be exploited to maintain the operating point of a fast amplifier in the hair cell bundle.

However, this possibility has recently been questioned Dallos for a number of reasons, one of which is the somatic motor protein, prestin, has an extremely fast response capability.

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So we did and she felt better. Travel American South. We may be able to get it on Adult Contemporary. Doug Addison is a prophetic speaker, author and coach. It was so genuine. Evidently the reason is not that the sound 'carries' better downwind, but that the turbulence of the upwind motion disrupts the air as an effective transmission medium.

So the interrelationships between hair cell motility and transduction, and between OHC and IHC remain an intense focus of current research. For low frequencies, it has been shown that an out-of phase motion exists between the IHC reticular lamina and the overlying TM so that electromechanical action of the OHC may stimulate the IHC directly, without involvement of the basilar membrane Nowotny and Gummer, The possible roles of the OHC and efferent systems are made more complex by recent findings of reciprocal synapses between OHC and their efferent terminals, seen as afferent and efferent synapses on the same fiber Thiers et al.

One explanation for this system is that the synapses may locally without involvement of the central nervous system coordinate the responses of the OHC population so that optimum operating point is maintained for high frequency transduction. The hysteresis was thought to result from active motor elements, either in the stereocilia or the lateral wall of the OHC, shifting the transducer function in the direction of the bias. A similar hysteresis was also reported by Lukashkin and Russell who proposed that a feedback loop was present during the bias that keeps the operating point at its most sensitive region, shifting it in opposite directions during compression and rarefaction phase of the bias tone thereby partially counteracting its effects.

If there are systems in the cochlea to control operating point as an integral component of the amplification process, they would undoubtedly be stimulated in the presence of external infrasound. The otolith organs, comprising of the saccule and utricle, respond to linear accelerations of the head Uzun-Coruhlu et al, and the semi-circular canals respond to angular acceleration. These receptors contribute to the maintenance of balance and equilibrium.

In contrast to the hair cells of the cochlea the hair cells of the vestibular organs are tuned to very low frequencies, typically below 30 Hz Grossman et al, Frequency tuning in vestibular hair cells results from the electrochemical properties of the cell membranes Manley, ; Art and Fettiplace, and may also involve active mechanical amplification of their stereociliary input Hudspeth, ; Rabbit et al. Although vestibular hair cells are maximally sensitive to low frequencies, they typically do not respond to airborne infrasound. Rather, they normally respond to mechanical inputs resulting from head movements and positional changes with their output controlling muscle reflexes to maintain posture and eye position.

At the level of the hair cell stereocilia, although vibrations originating from head movements and low frequency sound would be indistinguishable, the difference in sensitivity lies in the coupling between the source stimulus and the hair cell bundle. Head movements are efficiently coupled to the hair cell bundle, while acoustic stimuli are inefficiently coupled due middle ear characteristics and the limited pressure gradients induced within the structure with sound stimuli Sohmer In a similar manner to cochlear hair cells, which respond passively i..

The otolith organs have been shown to respond to higher, acoustic frequencies delivered in the form of airborne sounds or vibration. This has been demonstrated in afferent nerve fiber recordings from vestibular nerves Young et al. These responses arise because higher frequency stimuli are more effectively coupled to the otolithic hair cells.

But as sound or vibration frequency is reduced, its ability to stimulate the vestibular organs diminishes Murofushi et al. So for very low frequencies, even though the hair cell sensitivity is increasing as active tuning is invoked, mechanical input is being attenuated. While there have been many studies of vestibular responses to physiologic stimuli i. As people do not become unsteady and the visual field does not blur when exposed to high level infrasound, it can be concluded that sensitivity is extremely low. In some pathologic conditions, coupling of external infrasound may be greater.

Scorpions - Wind Of Change (8D SOUND)

To our knowledge, the sensitivity of such patients to controlled levels of infrasound has never been evaluated. In this respect, it needs to be considered that vestibular responses to stimulation could occur at levels below those that are perceptible to the patient. Todd et al. Some aspects of cochlear fluids homeostasis have been shown to be sensitive to low frequency pressure fluctuations in the ear.

The endolymphatic sinus is a small structure between the saccule and the endolymphatic duct which has been implicated as playing a pivotal role in endolymph volume regulation Salt The sinus has been shown to act as a valve, limiting the volume of endolymph driven into the endolymphatic sac by pressure differences across the endolymphatic duct Salt and Rask-Andersen, In contrast, the application of 5 cycles at 0. The pressure changes driving these pulses was large, comparable to those produced by contractions of the tensor tympani muscle, as occurs during swallowing.

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Tensor tympani contractions produce displacements of the stapes towards the vestibule for a duration of approximately 0. The lowest sound level that drives endolymph movements is currently unknown. A therapeutic device the Meniett: www. The infrasonic stimulus 6 Hz or 9 Hz is delivered by the device in conjunction with sustained positive pressure in the external canal. An important aspect of this therapy, however, is that a tympanostomy tube is placed in the tympanic membrane before the device is used. The tympanostomy tube provides an open perforation of the tympanic membrane which shunts pressure across the structure, so that ossicular movements and cochlear stimulation are minimized, and the pressures are applied directly to the round window membrane.

Nevertheless, the therapeutic value of this device is based on infrasound stimulation influencing endolymph volume regulation in the ear. As presented above, endolymphatic hydrops, by occluding the perilymph communication pathway through the helicotrema, makes the ear more sensitive to infrasound Salt et al, It has also been shown that non-damaging low frequency sounds in the acoustic range may themselves cause a transient endolymphatic hydrops Flock and Flock, ; Salt The mechanism underlying this volume change has not been established and it has never been tested whether stimuli in the infrasound range cause endolymphatic hydrops.

Although infrasound at high levels apparently does not cause direct mechanical damage to the ear Westin , Jauchem and Cook, in animal studies it has been found to exacerbate functional and hair cell losses resulting from high level exposures of sounds in the audible range Harding et al. This was explained as possibly resulting from increased mixture of endolymph and perilymph around noise induced lesion sites in the presence of infrasound.

Demonstrating an accurate frequency spectrum of the sound generated by wind turbines creates a number of technical problems. One major factor that makes understanding the effects of wind turbine noise on the ear more difficult is the widespread use of A-weighting to document sound levels.

A-weighting shapes the measured spectrum according to the sensitivity of human hearing, corresponding to the IHC responses. As we know the sensitivity for many other elements of inner ear related to the OHC do not decline at the steep slope seen for human hearing, then A-weighting considerably underestimates the likely influence of wind turbine noise on the ear.

In this respect, it is notable that in none of the physiological studies in the extensive literature reporting cochlear function at low frequencies were the sound stimuli A-weighted. This is because scientists in these fields realize that shaping sound levels according to what the brain perceives is not relevant to understanding peripheral processes in the ear. A-weighting is also performed for technical reasons, because measuring unweighted spectra of wind turbine noise is technically challenging and suitable instrumentation is not widely available.

Most common approaches to document noise levels conventional sound level meters, video cameras, devices using moving coil microphones, etc are typically insensitive to the infrasound component. Using appropriate instrumentation, Van den Berg showed that wind turbine noise was dominated by infrasound components, with energy increasing between Hz and 1 Hz the lowest frequency that was measured at a rate of approximately 5.

Sugimoto et al. In most studies of wind turbine noise, this high level, low frequency noise is dismissed on the basis that the sound is not perceptible. This fails to take into account the fact that the OHC are stimulated at levels that are not heard. 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.

Long term stimulation of position-stabilizing or fluid homeostasis systems could result in changes that disturb the individual in some way that remains to be established. We realize that some individuals such as fighter pilots can be exposed to far higher levels of infrasound without undue adverse effects. In this review, we have confined our discussion to the possible direct influence of infrasound on the body mediated by receptors or homeostatic processes in the inner ear. This does not exclude the possibility that other receptor systems, elsewhere in the body could contribute to the symptoms of some individuals.

Hearing perception, mediated by the inner hair cells of the cochlea, is remarkably insensitive to infrasound. Other sensory cells or structures in the inner ear, such as the outer hair cells, are more sensitive to infrasound than the inner hair cells and can be stimulated by low frequency sounds at levels below those that are heard.

The concept that an infrasonic sound that cannot heard can have no influence on inner ear physiology is incorrect. A-weighting wind turbine sounds underestimates the likely influence of the sound on the ear.