The Occurrence of Nocturnal Wind Farm Rumbling Noise

Nocturnal low-frequency noise from a wind farm was analysed in terms of its magnitude and amplitude modulation (AM) content. Acoustic and meteorological measurements were conducted at an unoccupied dwelling located 3.3 km from a wind farm. At times when the wind farm was operating at a capacity factor greater than 40% and the residence was downwind from the wind farm, low-frequency wind farm noise consistently exceeded the normal hearing threshold at 1/3-octave frequencies of 50 Hz and above. During these times, AM at the blade-pass frequency was found to be present at low frequencies. The AM was evaluated using the 'Reference' method that was recently introduced by the Institute of Acoustics in 2016. This method successfully identified AM most consistently when compared to other detection algorithms. The presence of AM was verified through reference to narrowband plots, which show AM as side-bands adjacent to the tonal frequency that is modulated. Based on the fact that the noise is shown to be both audible and contain potentially annoying AM, the potential for sleep disturbance is established. The implications arising from repeated arousals are discussed and include daytime sleepiness and impaired mood and function.