August 10, 2012
Connecticut, Noise, Regulations

Connecticut Siting Council Draft Wind Regulations

Ambrose, Stephen; and Rand, Robert

At the request of FairWindCT, Inc., we submit our professional opinions for the review of the proposed Connecticut Siting Council Draft Wind Regulations dated 12 April 2012. …

Industrial wind turbine noise has proven to be a source of public complaints for non-urban neighbors living up to a mile away. This is especially true in locations where wind speeds can be calm to light at ground level and strong at the turbine blade heights, and/or wind directions differ from low to high elevation. The change in wind speed and/or angle with increased elevation is called “shear”. Changes in topographical elevation produce “turbulence”. Shear and turbulence are strong in New England, but mild at manufacturer test locations where winds are steady and there are small changes in wind speed with increased elevation.

Comment 1: Wind shear and turbulence consideration is omitted.

Comment 2: Low-frequency noise consideration is omitted.

Wind turbine manufacturer test data is obtained and published with A-weighting (as required by the IEC 61400-11 standard). This is very misleading since A-weighting filters out low frequency noise contributions and excludes infrasonic energy. Data published by wind turbine manufacturers discounts the significance of low frequencies and infrasonic energy. Un-weighted (linear or “dBZ”) field measurements have confirmed that most of the acoustic energy produced by wind turbines is low frequency and infrasonic (below 200 Hz).

Low frequencies are a well documented common complaint for wind turbine noise; i.e., it sounds like “a jet plane that never lands”. This is especially true indoors, where the higher frequencies are blocked and the longer wavelengths of low-frequency and infrasonic energy pass easily through the through exterior walls and roof into the home. The predominance of low frequencies inside homes is a leading cause for complaints.

The proposed regulations should include mandatory considerations for wind turbine low frequency noise by requiring the inclusion of a maximum low frequency limit for proposed facilities. A maximum of 55 dBC, outdoors at night (measured using the broadband “dBC” filter found on professional sound level meters) has a growing consensus by environmental acoustic and public health professionals. …

Comment 3: Proposed requirements are too lax to protect neighbors from excessive noise and adverse public health and well-being impacts. As written these requirements would result in widespread complaints and strong adverse community reactions. These findings are supported by the long-standing, industry-recognized and accepted community noise assessment methodologies published by USEPA dating back to the 1970’s.

Comment 4: Proposed requirements continue to “noise level excursions” (exceedances) allowed under the existing Connecticut law. These “allowances” would intensify wind turbine noise impacts especially at night when most people are trying to sleep.

Comment 5: Setback distances for noise must be greater than proposed for safety.

A setback distance of 1.1 times the wind turbine height, or the manufacturers recommended safety setback distance, may be appropriate for mechanical failure of the turbine structure and break-away parts. The safety setback does not address noise impacts. A reasonable and appropriate setback for noise is at a minimum 10 times the turbine height. This is supported by actual in-situ noise level measurements made in the vicinity of industrial wind turbines.


Taking the WHO night-time maximum limit guideline of 40 dBA and applying the wind shear design safety factor of 5 to 8 dB reveals a more realistic and appropriate maximum nighttime noise limit of 32 to 35 dBA. These noise limits may be achievable using a minimum noise setback distance of 10 times the turbine height (tower base to maximum blade height). Wind turbines rated at up to 2 MW require a setback of approximately 1 mile which is supported by in-situ wind turbine noise measurements in quiet areas (under 30 dBA nighttime); protecting public health and welfare. Short-term noise excursions, allowed by the existing Connecticut law, have been associated with sleep disturbance and should be disallowed. Low-frequency noise produced by wind turbines must be limited and considered to be a critical factor for determining the viability for a proposed site to be a good acoustic neighbor.

Download original document: “Ambrose and Rand Comments on Connecticut Siting Council Draft Wind Regulations [1]

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[1] Ambrose and Rand Comments on Connecticut Siting Council Draft Wind Regulations: