BAD AXE – The sound made by wind turbines makes for a lot of heated discussion at public meetings in Huron County.
Jeff Smith, Huron County building and zoning director, clarified how much sound is allowed from the turbines last week before the Huron County Planning Commission.
He said the sound restrictions in Huron County’s wind ordinance are consistent with, or more restrictive than, the World Health Organization (WHO) standards.
“One thing we get questioned quite often on is how the county ordinance relates to the measure of sound for wind turbines at dwellings. You’ll hear a lot of people throw out the number 30 decibels,” Smith said. “They’re not reading the entire section of the World Health Organization report.”
In the report, that number refers to indoor noise.
But people at public meetings have quoted 30 decibels (dB) as the acceptable level of outdoor noise by the WHO.
“I think that causes some confusion,” Smith said.
The WHO Guidelines for Community Noise was published in 1999. The Executive Summary of that document states, “To protect the majority of people from being seriously annoyed during the daytime, the outdoor sound level … should not exceed 55 dB LAeq.”
Protection from being “moderately annoyed” requires a sound level not to exceed 50 dB LAeq.
The county wind ordinance requires nighttime levels outside to be at 45 dB LAeq at all times for nonparticipating landowners, and during night hours for participating landowners. Daytime sound levels must not exceed 50 dB LAeq for participating landowners.
That county ordinance number is measured within 50 feet of a home. The WHO number is measured three feet outside of the home.
“… The noise reduction from outside to inside with the window open is 15 dB,” according to the WHO.
If the outdoor sound equals 45 dB LAeq, that would make the indoor noise level 30 dB LAeq.
Bedrooms at night should be 30 dB LAeq, according to the WHO.
“To enable casual conversation indoors during daytime, the sound level of interfering noise should not exceed 35 dB LAeq,” according to the WHO community noise guidelines.
Sound limits for the county ordinance, as well as the WHO standards, are measured in “A-weighted continuous sound level (Leq),” as stated in the ordinance.
Both the county and WHO measure noise with the sound pressure meter set at “fast.”
This ensures, Smith says, that “we’re comparing apples to apples.”
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