Since the large-scale construction of wind power facilities in Japan, serious complaints have arisen from residents regarding wind turbine noise (WTN). However, there was insufficient scientific background to assess this issue. To address this situation, several research projects have been conducted by the Ministry of the Environment, Government of Japan. In this paper, we report actual WTN field measurements for these projects. The LAeq values of WTN ranged from 25 to 50 dB in residential areas. On the other hand, the residual noise levels in control areas with similar local characteristics to the wind farm areas but not affected by WTN ranged from 20 to 35 dB. Thus, there was a notable difference between WTN and residual noise. Wind power facilities are often constructed in quiet, rural districts. With regards to WTN, LAeq of noise caused by wind turbines as well as the increase in the overall noise level are important. The measurements of spectral characteristics of WTN were compared against the criterion curve to assess low-frequency noise. As a result, infrasound (frequency components below 20 Hz) for all measured WTN values in the residential (immission) areas were found to be much lower than the corresponding values on the criterion curve. In addition, amplitude modulation (AM) sound (also referred to as “swish sound”) is often associated with WTN, and can cause serious discomfort to nearby residents. The actual situation with regard to AM sound in residential areas located near wind farms was clarified by field measurements.
