Amplitude modulation: Difference between revisions
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A characteristic of wind turbine noise that makes it more [[Annoyance|annoying]] than other noises at the same average [[Decibel|sound level]] is its pulsing or throbbing “whoosh … whoosh”, which is called ''amplitude modulation'' (AM). | A characteristic of wind turbine noise that makes it more [[Annoyance|annoying]] than other noises at the same average [[Decibel|sound level]] is its pulsing or throbbing “whoosh … whoosh”, which is called ''amplitude modulation'' (AM). | ||
Most existing noise regulations – if they exist at all – use long-term average measures of sound levels | Most existing noise regulations – if they exist at all – use long-term average measures of sound levels, and thus fail to take AM into account. (They usually also fail to consider [[infrasound and low-frequency noise]], another characteristic that makes wind turbine noise more intrusive. In addition, Australian acoustician Steven Cooper[https://www.wind-watch.org/documents/simplified-method-for-determination-of-amplitude-modulation-of-audible-and-inaudible-wind-turbine-noise/] notes that AM may be “felt” like intrusive infrasound as it modulates at infrasonic frequencies.) | ||
In England a wind energy facility was approved with conditions including a [https://www.wind-watch.org/documents/den-brook-amplitude-modulation-condition/ definition] of unacceptable AM: any change, upon complaint, outside the dwelling, in LA<sub>eq,125ms</sub> of >3 dB in any 2-second period ≥5 times in any minute with LA<sub>eq,1min</sub> ≥28 dB and such excess occurring in ≥6 minutes in any hour, | In England a wind energy facility was approved with conditions including a [https://www.wind-watch.org/documents/den-brook-amplitude-modulation-condition/ definition] of unacceptable AM: any change, upon complaint, outside the dwelling, in LA<sub>eq,125ms</sub> of >3 dB in any 2-second period ≥5 times in any minute with LA<sub>eq,1min</sub> ≥28 dB and such excess occurring in ≥6 minutes in any hour. Or in other words: When the minute-long average noise level is 28 dBA or more, a 125-millisecond spike of 3 dBA or greater above the average noise level (3 dB being the difference in noise level detectable by the human ear<ref>[[Decibel]]</ref>) can not occur five or more times in any 2-second period in 6 or more minutes of any hour. | ||
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Revision as of 16:08, 20 December 2021
A characteristic of wind turbine noise that makes it more annoying than other noises at the same average sound level is its pulsing or throbbing “whoosh … whoosh”, which is called amplitude modulation (AM).
Most existing noise regulations – if they exist at all – use long-term average measures of sound levels, and thus fail to take AM into account. (They usually also fail to consider infrasound and low-frequency noise, another characteristic that makes wind turbine noise more intrusive. In addition, Australian acoustician Steven Cooper[1] notes that AM may be “felt” like intrusive infrasound as it modulates at infrasonic frequencies.)
In England a wind energy facility was approved with conditions including a definition of unacceptable AM: any change, upon complaint, outside the dwelling, in LAeq,125ms of >3 dB in any 2-second period ≥5 times in any minute with LAeq,1min ≥28 dB and such excess occurring in ≥6 minutes in any hour. Or in other words: When the minute-long average noise level is 28 dBA or more, a 125-millisecond spike of 3 dBA or greater above the average noise level (3 dB being the difference in noise level detectable by the human ear[1]) can not occur five or more times in any 2-second period in 6 or more minutes of any hour.