Pilot study on perceived sleep acceptability of low-frequency, amplitude modulated tonal noise

The global expansion of wind farm facilities has been associated with community complaints regarding sleep disturbance. This may be related to the presence of amplitude modulation (AM) in wind turbine noise (WTN), which has been shown to result in increased annoyance. However, at present, it is unknown whether acceptability for sleep is judged differently to annoyance or if AM may be more problematic for sleep than other noise types. Previous studies have also focused predominantly on 'swish' noise rather than tonal AM, where the latter has been more consistently measured at several wind farms in South Australia at distances greater than 1 km. Therefore, this study investigated the perceived sleep acceptability of WTN containing low-frequency tonal AM through listening tests involving 13 participants. A total of 13 noise stimuli were synthesised based on real recordings of WTN. The tonal audibility and AM depth were varied within a range relevant to the AM depth measured in field recordings. Participant responses were highly variable, but in self-reported noise-sensitive individuals, an increase in the AM depth at a tonal audibility of 12 dB(A) was associated with lower acceptability for sleep.