Infrasound From Wind Turbines Could Affect Humans

Author: Salt, Alec; and Kaltenbach, James | Health, Noise

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Abstract
Wind turbines generate low-frequency sounds that affect the ear. The ear is superficially similar to a microphone, converting mechanical sound waves into electrical signals, but does this by complex physiologic processes. Serious misconceptions about low-frequency sound and the ear have resulted from a failure to consider in detail how the ear works. Although the cells that provide hearing are insensitive to infrasound, other sensory cells in the ear are much more sensitive, which can be demonstrated by electrical recordings. Responses to infrasound reach the brain through pathways that do not involve conscious hearing but instead may produce sensations of fullness, pressure, or tinnitus, or have no sensation. Activation of subconscious pathways by infrasound could disturb sleep. Based on our current knowledge of how the ear works, it is quite possible that low-frequency sounds at the levels generated by wind turbines could affect those living nearby.

Figure 1. Upper Panel: Full-spectrum recording of sound from a wind turbine recorded for 20 seconds in a home with the wind turbine 1,500 ft downwind (digital recording kindly provided by Richard James). Lower Left Panel: Result of high-pass filtering the waveform at 20 Hz, showing the sound that is heard, including the sounds of blade passes. Lower Right Panel: Result of low-pass filtering the waveform at 20 Hz, showing the infrasound component of the sound.

Figure 4. Low-frequency components of wind turbine sound spectrum (below 1 kHz) before and after A-weighting. The original spectrum was taken from Van den Berg (2006). The shaded area represents the degree of alteration of the spectrum by A-weighting. A-weighting (i.e., adjusting the spectrum according to the sensitivity of human hearing) has the effect of ignoring the fact that low-frequency sounds can stimulate the outer hair cells [OHC] at levels that are not heard. Representing this sound as 42 dBA, based on the peak of the spectrum, ignores the possibility that low-frequency components down to frequencies as low as 5 Hz (from Figure 3) are stimulating the OHC. Also shown are the spectra after G-weighting (dotted) and C-weighting (dashed) for comparison.

Alec N. Salt
Washington University, St. Louis, Missouri, USA, salta/ent.wustl.edu

James A. Kaltenbach
Lerner Research Institute/Head and Neck Institute, Cleveland, Ohio, USA

Bulletin of Science, Technology & Society 31(4) 296–302 © 2011 SAGE
DOI:10.1177/0270467611412555

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