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Synopsis of Assessing Intrusive Noise and Low Amplitude Sound

Dr Bob Thorne


The sound from a wind farm is essentially of an intrusive nature and is of low amplitude. That is, it is not very loud and it has varying character depending on wind speed and direction. This Paper presents a synopsis of the methodology to assess low amplitude intrusive noise with respect to an individual. The methodology has unique practical application in wind farm noise analysis as it combines human perception with sound measurement and a process to integrate disparate information into a meaningful whole, as illustrated in Figure 1.

The methodology presented in Figure 1 is in three parts:

  1. The first part is data gathering: a sound is analysed in a structured, standard manner for its acoustic and sound quality characteristics. The person who is interested in the sound is able to undertake a series of environmental and noise sensitivity tests to evaluate personal sensitivity and perceptions regarding the sound.
  2. The second part is data processing: The sound quality measures and personal perceptions are integrated into a structured analytical methodology referenced to subjective analysis and objective criteria for which the relativities between non-parametric and parametric data are structurally encapsulated.
  3. The third part of the methodology calculates an intrusive noise rating: The information derived from the first two parts of the methodology is structured into a decision process for sound and intrusive noise, with special consideration given to low amplitude sound analysis.

Sound is NOT noise. Sound is a physical construct or measure of sound pressure level. Noise, however, is how a person perceives specific sounds. This emphasis on definition is very important because it is the character, as well as the sound level of the sound from wind turbines that determines whether the 'noise' is reasonable or unreasonable.

Noise is often quoted as being 'unwanted sound.' This definition is meaningless.




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