Comparison of the IOA method and Japanese F-S method for quantitative assessment of amplitude modulation of wind turbine noise - A study based on the field measurement results in Japan

摘要

Amplitude modulation sound is generally contained in wind turbine noise (WTN), and often causes serious annoyance in the neighboring areas around wind farms. Therefore, it is very important to establish the method to evaluate the extent of amplitude modulation. In actual conditions, WTN varies slowly being affected by meteorological conditions and the depth of the amplitude modulation (peak-trough difference) varies and its time-averaged level also fluctuates slowly as a trend. To deal with amplitude modulation sound with such temporal characteristics, the authors proposed the "F-S method" in which the level difference between the A-weighted sound pressure levels obtained by Fast time-weighting and Slow time-weighting is firstly calculated and the amplitude modulation depth (D_(AM)) is evaluated as the 90% range of the level difference signal. On the other hand, the Institute of Acoustics (IOA) has published the final report regarding the assessment of amplitude modulation sound, in which rather sophisticated signal processing techniques are applied to assess the extent of amplitude modulation (the IOA reference method). By applying the F-S method and the IOA reference method to the WTN data obtained at 66 measurement points around 11 wind farms in Japan, the correspondence of the results obtained by the two methods were examined.