Acceptability of amplitude modulated tonal wind farm noise for sleep: a laboratory study

This study investigated self-reported sleep acceptability of wind farm noise (WFN) containing low-frequency amplitude modulated tones during evening listening tests in an acoustics and sleep laboratory. A range of 29 WFN samples with and without low-frequency amplitude modulated tonal noise were synthesised and delivered via headphones to participants who were asked to adjust the sound pressure level to the highest level they felt was acceptable for sleep. Fifty-five participants were recruited from four groups; N = 8, living <10 km from a wind farm and reporting WFN related sleep disruption; N = 18, living <10 km from a wind farm and reporting no WFN sleep disruption; N = 15, reporting road traffic noise (RTN) related sleep disruption; and N = 14 control participants living in a quiet rural area. In general, participants had normal hearing and were aged between 18 and 80 years. The WFN disturbed group overall mean acceptable sound pressure level for sleep was 33.9 dBA, which was the lowest among groups and 10.7 dBA (95% confidence interval, 7.9–13.6) lower than for the control group. There were negligible differences in acceptable levels for sleep of low-frequency amplitude modulated tonal wind farm noise compared to the reference sample, which was the same stimulus without tonality or amplitude modulation. Only the participant group reporting RTN related sleep disruption preferred lower noise levels for the amplitude modulated tonal wind farm noise compared to the reference sample (mean −1.4 dBA, 95% confidence interval: −2.7–−0.1).