Rob Rand is a professional acoustician with decades of experience. On February 5, 2011 he was part of a community presentation about wind turbines and their effects at the Blissfield Middle School, Michigan. If you have just one hour to spend learning about wind turbines and noise, listening to his presentation would be a good way to spend it. The other presentations were also very good and well worth the time if you want to learn something about wind turbines.
Most of what he said wasn’t particularly new to me, having studied this stuff for over 3 years now. One point that was new was a study on community response to noise that was published by the EPA way back in 1974, way before wind turbines were on anybody’s radar. Using their criteria, which were primarily developed for road and especially aircraft noise, it becomes easy to see why the residents are so upset with wind turbines.
The EPA’s report is titled INFORMATION ON LEVELS OF ENVIRONMENTAL NOISE REQUISITE TO PROTECT PUBLIC HEALTH AND WELFARE WITH AN ADEQUATE MARGIN OF SAFETY [backup link] and while it wasn’t itself a regulation, it influenced any number of states when they drew up their regulations. The section that Rand mentioned is in Appendix D, starting on page D-16. They present a model, based on an even earlier U.S. Air Force study, where there are 7 factors that influence a community’s reaction to a new noise source, page D-17. They correlated the actual level of community complaints to these 7 factors and were able to predict pretty well the reaction of the community to a new noise source.
The chart showing this is shown below, Fig D-7, page D-20.
Initially, the levels involved would seem to indicate that wind turbines shouldn’t be much of an issue. After all, you don’t get into “vigorous action” (meaning lawsuits) until you hit about 75dB, and wind turbines are probably never that loud. The key to this puzzle is “NORMALIZED”. The levels on this chart are for “residential urban” environments. To get them back to their equivalent rural levels, you have to apply the Corrections in Table D-7, page D-18. By my count, there’s a total of 20dB that should be subtracted from the chart’s levels.
The typical U.S. limits are 45dB, but that is based on computer modeling performed by the proponents. Actual measurements indicate the noise levels can be anywhere up to 65dB at typical setback distances. If the threshold for legal action is 55dB (75 minus 20) you can see where the problem is.
Another way to look at it is how much the ambient noise level is increased. On page D-20 the report mentions “…vigorous community action may be expected when the excess approaches 20dB”. Given typical rural ambients in the mid-20’s, especially at night, it is a no-brainer that even 45dB will get people calling their lawyers.
Mars Hill and Freedom, both in Maine, are presently in court. Vinalhaven may get there soon enough. Even 37 years ago this was entirely predictable.