Engineer talks to Orleans wind panel about noise
LAFARGEVILLE — An acoustic engineer told the town of Orleans wind committee that low-frequency noise needs to be measured and controlled as part of any zoning ordinance created.
Charles E. Ebbing, retired engineer with Carrier Corp. with nearly 50 years’ experience, explained the source and stress effects of low-frequency noise to the committee, which met Tuesday night. Low-frequency noise ranges from a few thousand hertz down to nearly zero hertz.
“A house shuts out all high-frequency noise and allows in only low-frequency,” he said. “The noise level of low-frequency can be greater inside than outside, because of the resonance inside buildings.”
He observed that very few acoustical engineers have worked on low-frequency noise.
Besides the decibel level, Mr. Ebbing pointed to other types of problems with noise.
“The meter doesn’t measure what you hear,” he said. “It measures the energy of the sound pressure. It doesn’t measure annoyance, only loudness. It doesn’t measure quality.”
Mr. Ebbing said that heating and air conditioning systems often are required to be quieter if they have an impulsive or tonal quality.
He said measurements of both audible, or dBA, and low-frequency, or dBC, noise should be conducted. Those measurements then should be compared to each other by subtracting dBA from dBC. If dBC is greater than dBA by more than 25 decibels, the noise will have a rumbling quality.
In working with air conditioning systems, Mr. Ebbing has seen the effects of low-frequency noise. He said that its rumbling quality increases stress, distraction and, in homes, sleeplessness.
He said a law to protect people should include initial measurements, compliance checks afterward and regular monitoring as the years pass.
Mr. Ebbing reiterated that ambient background noise in rural areas is as low as 24 decibels at night. According to the wind industry, a typical wind farm is about 44 decibels at 1,500 feet. So the noise at night would be increased by about 20 decibels.
Noise explanations from the wind industry say rural areas are quiet when there is no wind and turbines don’t generate power when there is no wind.
“They’re implying that when the wind is blowing and the turbines move, they will create noise but there will be other noise to cover it,” Mr. Ebbing said. “They’re wrong in that most of the time we can have no wind blowing at the ground but have wind higher up, so wind turbines can turn when we don’t have other noise at the ground.”
The next committee meeting will be at 7 p.m. April 14 at the town offices.
By Nancy Madsen
Times Staff Writer
26 March 2009
Tags: Wind power, Wind energy
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