Perception-based protection from low-frequency sounds may not be enough
Alec N. Salt and Jeffery T. Lichtenhan|August 14, 2012
Dr. Alec Salt, a expert on human ear physiology at the Cochlear Fluids Research Laboratory of Washington University in St. Louis examined the effect of low-frequency, inaudible sound, on human health. In particular, Dr. Salt investigated the very low frequency sounds and infrasound (below 20 Hz) produced by industrial-scale wind turbines. His paper as presented at the Inter-sound 2012 conference can be accessed by clicking on the link(s) at the bottom of this page.
Dr. Alec Salt, a expert on human ear physiology at the Cochlear Fluids Research Laboratory of Washington University in St. Louis examined the effect of low-frequency, inaudible sound, on human health. In particular, Dr. Salt investigated the very low frequency sounds and infrasound (below 20 Hz) produced by industrial-scale wind turbines. His paper as presented at the Inter-sound 2012 conference can be accessed by clicking on the link(s) at the bottom of this page.
The following is an excerpt of Dr. Salt's conclusion as it appears in his paper:
It is well documented that people find noise with prominent low frequency content
annoying. In the context of wind turbine noise it is known that the larger wind turbines can generate high levels of low frequency noise and infrasound. The concern arising from the work we report here is that the cochlear apex of people exposed to such low-frequency sounds will be stimulated to a far greater degree than is suggested by their measured A-weighted sound level. The demonstration that sounds in the range of 40 – 45 dB A may be causing intense stimulation of the cochlear apex has not previously been appreciated. This may account for why the influence of low frequency noise on humans is greater than that estimated from spectral measurements and why consideration of noise crest factors is appropriate. The fact that apical stimulation is maximal when mid- and high-frequency components are absent from the sound may also be important to wind turbine noise effects. It is known that people’s houses attenuate sound frequencies in the audible range but have little influence, or may even increase infrasound and low-frequency sound levels. Thus, prolonged periods of exposure to wind turbine noise in an otherwise quiet environment (such as a quiet bedroom) seems to represent a condition in which apical stimulation would be maximized.
Intense stimulation of the cochlear apex will certainly have some influence on human physiology. On this basis we think that the concept of “what you can’t hear can’t hurt you” is false. Similarly, there are potential mechanisms by which low-frequency sounds could influence vestibular physiology which are being ignored by some. Our measurements showing that the ear generates large electrical responses to low-frequency stimulation suggest that the effects of low-frequency sound on people living near wind turbines should not be dismissed by those with little understanding of how low frequency sounds indeed affect the ear. More research on this topic is necessary to enlighten the scientific, medical, and legal communities, and the public, some of whom are being chronically exposed to these sounds.
