The Use of Noise Perception Index (NPI) For Setting Wind Farm Noise Limits

Malcolm Hunt , Lindsay Hannah

New Zealand Acoustics, 22(3), pp.20- 25 . (2009).

This paper investigates Noise Perception Index (NPI) as a method for assessing environmental noise from wind farms. NPI is a newly emerging noise assessment tool based on the degree to which pre-existing ambient background sound levels (LA90) are exceeded by the sound under investigation, in this case, wind farm noise. A practical use of NPI is in the setting of wind farm noise limits. Typically wind farm noise limits of LAeq 40 dB are recommended as an upper limit for wind farm noise received at residential sites by the New Zealand Wind Turbine Acoustic Standard, NZS6808:1998 Acoustics – The Assessment & Measurement Of Sound From Wind Turbine Generators however lower limits may be justified at certain locations, under certain conditions. NPI can assist by identifying sites which exhibit those conditions