Page 52 - Volume 12, Issue 2 - Spring 2012

WIND TURBINES AND GHOST STORIES:
THE EFFECTS OF INFRASOUND ON THE HUMAN AUDITORY SYSTEM
Hsuan-hsiu Annie Chen
Neuroscience Undergraduate Program University of California, Los Angeles Los Angeles, California 90095
and
Peter Narins
Departments of Integrative Biology & Physiology, and Ecology & Evolutionary Biology University of California, Los Angeles
Los Angeles, California 90095
Introduction
“...studies provide strong
and geographical placements are neces- sary to minimize community exposure and potential human health risks.
Infrasound definition
It is popular belief that the audio frequency range of human hearing is from 20 to 20,000 Hz and that anything beyond these limits is undetectable by humans. Infrasound is the term that
Climate change and fossil fuel
depletion have pushed many
countries to seek and invest in
alternative clean energy sources, such
as wind energy. By converting kinetic
energy from the wind into mechanical
or electrical energy, wind farms in
California, for example, power nearly
850,000 households each year, while
producing negligible green house gases and contributing little to water pollution1 (see Fig. 1). Nevertheless, several ecological and environmental concerns remain. High levels of infrasound and low frequency sounds generated by wind turbines pose a potentially serious threat to communities near wind farms. Wind energy companies remain largely dismissive, claiming that wind turbine noise is subaudible, undetectable by humans, and therefore presents minimal risk to human health. However, various cochlear micro- phonic, distortion product otoacoustic emission, and func- tional magnetic resonance imaging (fMRI) studies have demonstrated the detection of infrasound by the human inner ear and auditory cortex. Additional psychosomatic stress and disorders, including the “wind turbine syn- drome” and paranormal experiences, are also linked to infrasound exposures.2,3 With wind turbines generating sub- stantial levels of infrasound and low frequency sound, mod- ifications and regulations to wind farm engineering plans
evidence for infrasound
impact on human peripheral
and central auditory
responses.”
describes the “inaudible” frequencies below 20 Hz. Such a belief is based on the steep slope of hearing thresholds toward
4,5
At 1 kHz, the sound pressure level (SPL) necessary to perceive a 10 phon sound is 10 dB SPL. At 20 Hz, the minimum SPL for 10 phon sound perception has increased to about 84 dB SPL. The phon is a unit that describes perceived loudness level. With decreasing frequencies, the SPLs necessary for sound percep- tion increase rapidly, making very low frequencies at a nor- mally audible intensity more difficult to detect than higher frequencies of the same intensity. Humans’ lack of sensitivity to low frequencies is also reflected in the compression of hearing thresholds. At 1 kHz, the SPLs capable of triggering hearing range from 4 to more than 100 dB SPL, exceeding 100 dB in span and increasing at 10 dB/phon. In contrast, the SPL range at 20 Hz is from approximately 80 to 130 dB SPL,
the lower end of the human hearing range.
4 spanning only about 50 dB and increasing at 5 dB/phon. In
other words, a relatively small increase in SPL at 20 Hz would
Fig. 1. San Gorgonio Pass Windfarm in Riverside County, California. With more than 2,000 wind turbines installed, this windfarm produces enough electricity to power
Palm Springs and the entire Coachella Valley.
28
Photograph by Annie Chen
Wind Turbines and Ghost Stories 51