Summary. Public policy decisions about wind turbine noise face several challenges caused by the “variability factor.” Most sound ordinances are based on an average sound level, while neighbor responses are generally based on shorter-term peak noise levels, along with the additional variability in the sound quality of wind turbine noise; increasingly, complaints arise around projects that meet average sound level criteria. At the community scale, different types of communities may be more or less tolerant of moderately audible wind turbine noise in their rural environments; working farmers and ranchers often consider such noise trivial, while people in towns where more of the population is seeking peace and quiet may find the same noise intrusive. On the landscape scale, of course, atmospheric conditions can have dramatic effects on sound propagation, absorption, and audibility. Perhaps most importantly, real-world source levels of individual turbines can also vary greatly from idealized sound power levels used in sound modeling—minor wear, wind shear (especially directional), and inflow turbulence from nearby turbine wakes or atmospheric turbulence, can all increase the sound output of individual turbines. Both the transient peak sound levels caused by increased source levels and the variability in the sound quality, especially in turbulent conditions, are likely key drivers in community responses to wind turbine noise. This paper reviews publications that quantify aspects of wind turbine sound variability.
Presented at the 5th International Conference on Wind Turbine Noise, Denver, 28-30 August 2013
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