It is no easy trick to calculate sound levels from wind farms, or even to measure them. Consider a siren. It is basically a point source of sound, but with some preference for sending the sound out in a cone but not as much sound behind. In any case, if you double the distance from the siren, the sound intensity (in units of watts per square meter) is cut to one quarter. The siren is made so as to have a profound effect on the ear, and it accomplishes that by having its maximum intensity in the part of the spectrum where the ear hears well. A wind turbine produces sound both in the machinery at the hub and throughout the length of the blades. It is not a point source of sound except to somebody who is far away. A wind farm having many wind turbines spread out over many square miles is a broad source. The readings on a sound-level meter will not vary all that much whether you are at the base of a tower or out in the field. The frequency spectrum of noise from wind turbines contains some medium-high frequencies (whish!) from the blades passing through air, some machinery noises that are in the medium-low frequency range, and some ultra-low frequencies (whump-whump) as the blades pass by the supporting tower. (There is an interruption of the stream flow as each blade passes by.) I drove out to the Lamar wind farm this summer on a day that turned out to be mildly windy; the turbines were all turning. I took photographs from many places. (The turbines are 1.5 ME GE units; see attached picture) I could hear the machinery noise, something like you hear in a standard transmission. It was not an oppressive noise, though it might become one if you had to hear it day and night. It wasn't windy enough for the blades to produce much noise. The higher frequencies die out quickly with distance. Think of being a half-mile from a rock concert (which is closer than I like to get). All you can hear is the low frequencies, the bass tones, because they are the ones that diffract around all obstructions (low frequencies have long wavelengths). In the 70s, the government built a large wind turbine on a hilltop near Boone, NC. A friend visited there looking for a job at the college, and found that the residents hated that wind turbine. It was not the noise that was bothersome, but that the low frequency thump-thump was transmitted to the ground and felt earthquakish. Here was a case where a sound-level meter (which hears audible frequencies) would say there's no problem, but there was an irksome vibration. A sound-level meter would also pick up very little a half-mile from a rock concert, but you'd be able to tell it's there. An array of fifty (say) wind turbines producing unsynchronized thump-thump would not be as noticeable as the steady beat from a rock concert. In my view, the best evidence you might be able to muster would not be from meters but from residents who live night and day near a wind farm. Cheers, Howard --- Howard Hayden The Energy Advocate PO Box 7595 Pueblo West CO 81007 The Solar Fraud has sold out! The 2nd edition is on the way http://www.energyadvocate.com corkhayden@comcast.net Please note new e-mail address See also: www.valeslake.com for books fax: (719) 547-7819 George Washington: "Government is not reason, it is not eloquence, it is force. Like fire, it is a dangerous servant and a fearful master."