1 This Standard covers the prediction of sound from wind turbine generators (WTGs), the measurement of sound from WTGs, and the assessment of the received sound. It is designed to provide a level of investigation and reporting that may be specified by land use planning procedures under any relevant legislation (e.g. an act of Government/bylaw of Territorial Government), particularly the assessment of environmental sound. For the purposes of this Standard, sound is defined as being airborne vibration within the audible frequency range. See note below.
2 This Standard is applicable to both horizontal and vertical axis wind turbines that are used for the purpose of generating electricity i.e. WTGs, including ancillary equipment in the immediate vicinity of the turbines. Sound sources not in the immediate vicinity may be more appropriately measured and assessed using other Standards (see list of Related documents). This Standard does not address wind turbines used for water pumping or milling purposes, nor does it address sound from service equipment used at the windfarm for maintenance and construction.
3 This Standard deals specifically with the measurement of sound from WTGs in the presence of wind, a situation which has high potential for fluctuations and errors due to both increased background sound levels and wind effects at the microphone. The measurement of sound in the outdoor environment can produce reasonably accurate and repeatable results if the recommended procedure is followed. Measurements conducted in accordance with other more general Standards (e.g. NZS 6801) should not be used for the measurement of sound arising from WTGs themselves. However NZS 6801 needs to be referenced for measuring background sound and other matters as described in 4.5 of this Standard.
NOTE - WTGs may produce sound at frequencies below (infrasound) and above (ultrasound) the audible range. Ultrasound attenuates rapidly over moderate distances. Reference to overseas studies on infrasound reveals that:
(a) Sound spectra for modern WTGs indicate that compliance with the limits in this Standard (clause 4.4.2) will ensure that infrasound pressure levels will be well below the threshold of perception.
(b) Any potential adverse effect of infrasound would occur at levels greater than the threshold of perception (see Related documents).