Wind Power: Where Eagles Don’t Dare - Environmental Impacts of Renewable Energy - page 22

Noise is commonly defined as any unwanted sound. Based on the author's observa-
tion of the operation of wind farms in Washington, Oregon, California, Indiana, West
Virginia, North Dakota, South Dakota, New Mexico, and Wyoming, turbine-gener-
ated noise can be characterized as ranging from the swooshing sound of rotating rotor
blades to a deep, bass-like hum produced by a single operating wind turbine. Using a
calibrated sound pressure level (SPL) decibel (dB) measuring device, the author deter-
mined that the wind turbine-generated noise monitored and measured varied depend-
ing on the size of the turbines, their location, and distance away from the turbine or
wind farm. To better comprehend the material presented in this section, it is important
to have a fundamental knowledge of noise, sound, and the properties involved. Thus,
in the following section a basic introduction of noise and sound properties is presented.
Noise Basics
High noise levels are a hazard to anyone within hearing distance. High noise levels
are a physical stress that may produce psychological effects by annoying, startling,
or disrupting concentration, which can lead to accidents. High levels can also result
in damage to hearing, resulting in hearing loss. When wind farms are taken into con-
sideration, the noise produced has the potential to escalate into a severe nuisance for
small, local populations. This impact alone can have detrimental effects on a wide
range of related aspects including health and property values.
Noise and Hearing Loss Terminology
Many specialized terms are used to express concepts in noise, noise control, and
hearing loss prevention. The individual or group concerned with wind turbine noise
pollution and its potential impacts should be familiar with these terms. The National
Institute for Occupational Safety and Health (NIOSH, 2005) definitions below were
written in as nontechnical a fashion as possible:
Acoustic trauma —A single incident that produces an abrupt hearing loss.
Welding sparks (to the eardrum), blows to the head, and blast noise are
examples of events capable of providing acoustic trauma.
Action level —The sound level that, when reached or exceeded, necessitates
implementation of activities to reduce the risk of noise-induce hearing loss.
OSHA currently uses an 8-hour, time-weighted average of 85 dBA as the
criterion for implementing an effective hearing conservation program.
Aerodynamic noise— Generated noise; noise of aerodynamic origin in a mov-
ing fluid arising from flow instabilities.
Attenuate— To reduce the amplitude of sound pressure (noise).
Attenuation, real ear attenuation at threshold (REAT) —A standardized
procedure for conducting psychoacoustic tests on human subjects, it is
designed to measure the sound protection features of hearing protective
devices. Typically, these measures are obtained in a calibrated sound field
and represent the difference between subjects' hearing thresholds when
wearing a hearing protector vs. not wearing the protector.
Attenuation , real-world —Estimated sound protection provided by hearing
protective devices as worn in “real-world” environments.