here is an interesting explanation for why wind turbines are silent when standing underneath, but are very intrusive at a distance:
Re: Something In The Air
Sunday Telegraph Letters
Tony Middleton
12 September 2004
Your correspondent replying to David Bellamy's letter on wind farms says that he cannot hear any noise when standing underneath the blades of a wind turbine (Letter, Sep 5). This is a phenomenon well understood by developers who will encourage anyone threatened by a wind farm to seek out a convenient turbine and stand underneath it to satisfy themselves that there is no noise problem and thus no cause to object to their plans.
The reality of the matter is somewhat different. The noise perceived by those living within a mile or more of a wind farm, and particularly if downwind, is caused by the pressure wave that is generated each time a turbine blade passes the mast. For a single turbine these broad-band pressure fluctuations are not excessively intrusive, but where several turbines operate in proximity the pulses move into and out of phase, creating a doubling, tripling or more in the sound level, depending on how many turbines are grouped together.
Several low-magnitude pulse trains thus cause noise with an unexpectedly strong impulsive character whenever they synchronise. This is inaudible close to each individual turbine but is known to be the cause of considerable distress at greater distances. The effect is much more noticeable at night due to the greater differential between air flow at ground level and hub height and also the greater sound-carrying capability of the cooler night air.
The wind industry and the Department of Trade and Industry are not unaware of the problem but prefer to ignore it. Instead, they rely on research completed in 1997 that has little relevance to the serious low-frequency noise problems arising from the latest generation of monster wind turbines. This is disgraceful but sadly symptomatic of the whole wind power ethos".
....and another letter from somone actually living near a wind farm
The Pendleton Times
3 March 2005, p. 4
A letter from Linda Cooper quotes a resident of Tucker County, WV, as follows:
"I live in Tucker County approximately 1.5 miles from the Backbone Mountain wind turbines and have tried everything to get used to them. A brief visit to one of the viewing areas certainly gives no true impression of what it is like be forced to live with them. We have now suffered for three long years under their hideous shadows. They have taken over the entire landscape and are in our sight no matter where we go day or night, 24 hours a day, 365 days a year. The movement is impossible to ignore no matter how hard we try and the noise they make travels miles and miles down the mountains and hollows disturbing people who cannot even see them from their homes. I compare the noise to Chinese water torture or fingernails on a chalkboard or water dripping in a pan. Even on the calmest nights the endless drumming goes on; windows closed, pillows over the head, it is still inescapable. While we were led to believe this would be a clean, quiet, pristine, and environmentally-friendly way to address energy problems and give a huge boost to our ailing economy, I feel we have been tricked. There appears to be no recourse or plan to compensate us for property value losses, erosion of our quality of life, or mental anguish. Besides these 44 wind turbines, thousands more are in the pipeline! God help us!"
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