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Infrasonic noise not considered

Stacey Reid’s letter (Vacuum is louder than a turbine, June 28) shows a misunderstanding of what a “dB” is and how it is measured, which leads to easy acceptance of the “noise, what noise?” position of wind farm proponents.
A “dB” is a decibel – a measure of sound energy of any range – perhaps speech, bass speakers, vacuum cleaner noise or an earthquake. Our ears hear a only certain range of that energy – call it the “middle” range, including bagpipes, arguing couples and vacuum cleaners.
Community noise standards are based on sounds in the middle range, mainly because they are enforceable with inexpensive and easy-to-operate sound level meters. In sound measurement, this is called the “A” range and the measurements should read “dBA.”
Above and below that range, progressively, we hear little or nothing. Bats squeak in the “high” range. In the “low” range, we feel bass as well as hear it – it may nauseate us if it’s too loud.
Noise complaints about bass are more difficult to administer than sounds in the “A” range, as many communities have found, because they don’t necessarily show up on the sound meter.
But what about wind turbines? The majority of the noise they make is in the deepest “infrasonic” range, measured as “lin” – below bass, below hearing – and only measurable with expensive equipment by trained technicians. A study by NASA shows that the infrasonic part of the noise of turbines is about 55dB louder than the “A” part that a conventional meter would display.
So, if the meter reads 40dBA, the infrasonic noise can be 95dB. Although inaudible, this noise is experienced by the body in other ways that may be more akin to a continuous earthquake than to a refrigerator.
The doctors will have to weigh in on the health effects of these inaudible sound energies at strong levels over continuous periods of time, but the reference to community standards excludes the more relevant facts.
By comparison, although we can’t see the UV range of sunlight, we’ve learned the consequences of exposure and take precautions accordingly.
Dave Clark,
Shelburne