Perceived sleep acceptability of broadband amplitude-modulated wind farm noise

Amplitude modulated windfarm noise, also known as “swish” noise, is known to be annoying and associated with community complaints regarding sleep disturbance. While annoyance listening tests are common, tests for assessing sleep acceptability are lacking and the aim of this paper is to present such a method for rating sleep acceptability. Thirty-six participants (mean age ± SD (53±18), 20 female) underwent testing in a sleep laboratory before their bedtime. Sleep acceptability was measured by allowing participants to adjust stimuli noise levels to the loudest acceptable level for sleep, while lying in bed, for seven 3-minute long amplitude modulated wind farm noise stimuli. The stimuli contained amplitude modulation depths varying from 2 to 12 dB in steps of 2 dB. Sleep acceptability was shown to be lowest for baseline noise levels below 35 dBA and modulation depths greater than or equal to 10 dBA. For such stimuli, the maximum suggested penalty is 7 dBA. These results are in broad agreement with previous daytime annoyance results, emphasising the potential disturbance caused by amplitude modulation and the need to penalise this special audible characteristic of wind farm noise.