A recently published study implies that wind turbines as close as 0.25 mile and up to an outdoor average noise level of 46 dB(A) do not disturb sleep. In fact the actual noise levels were only estimated and averaged only 35.6 dB(A), which is a level that indeed would be unlikely to disturb sleep indoors. Furthermore, the range of distance from wind turbines extended to 11.22 kilometers. The result is that the data from households closer to noisier wind turbines are obviously diluted by the greater amount of data from farther away. Finally, averaging sleep experience over time serves to mask, rather than discover, any experience of particularly disturbing nights.
When the full paper is available, it will be interesting to see if the authors acknowledge these limitations: that their sample size from noisier and closer sites was insufficient to reach any conclusions, that noise levels were outdoors only and estimated rather than measured, and that sleep disturbance was assessed as 30-day averages, ignoring actual nightly experience.
Sleep. 2015 Oct 22.
Effects of Wind Turbine Noise on Self-Reported and Objective Measures of Sleep.
Michaud DS, Feder K, Keith SE, Voicescu SA, Marro L, Than J, Guay M, Denning A, Murray BJ, Weiss SK, Villeneuve PJ, van den Berg F, Bower T.