How annoying is wind-turbine noise?

As the harnessing of wind power as a renewable energy source has grown, so too has the debate over possible sleep loss and other physiological effects from the noise generated by wind turbines. Primarily arising in aerodynamic boundary layers along the rotating turbine blades, the sounds are amplitude modulated, with a characteristic “swish” at a frequency of about 1 Hz. Periodic sounds are more readily perceived than constant noise sources (see, for example, Physics Today, August 2013, page 19 ). Indeed, studies report that people are more likely to be annoyed by low levels of turbine noise than by much louder noise from transportation and other industrial sources. The degree of annoyance from turbine noise shows little correlation with the average sound level, termed the equivalent continuous sound-pressure level, yet that parameter is commonly used in noise regulations. To better understand the perception of turbine noise, Yeolwan Seong, Soogab Lee, and colleagues from Seoul National University have studied different ways of parameterizing the sounds. The researchers had test subjects in an anechoic chamber listen to simulations of wind-turbine noise at varying distances and orientations; for each sample, the subjects recorded their degree of annoyance on a seven-point scale. The team found that the listeners’ responses were best explained statistically not by the average sound level or fluctuation level but by the maximum instantaneous sound level, a parameter frequently used in criteria regulating nighttime (and some daytime) intermittent noise sources. (Y. Seong et al., J. Renewable Sustainable Energy 5, 052008, 2013.)