Analysis of unweighted low frequency noise and infrasound measured at a residence in the vicinity of a wind farm

Abstract

To characterise the noise at several residences located nearby a South Australian wind farm, time-data files as well as the third-octave spectra have been measured indoors and outdoors using low-frequency microphones fitted with various wind shields. Five consequative nights of data have been analysed and four cases are presented here to highlight the importance of atmospheric stability and the relative wind direction between the wind farm and a residence on the measured results. In the downwind cases, two low frequency tones were detected around 28 Hz and 46 Hz and significant levels of amplitude modulation of these tones at the blade pass frequency were observed. This amplitude modulation was most prominent when atmospheric conditions were stable. The presence of these tones and the associated amplitude modulation was also observed in the vibration results, however another amplitude modulated tone at 16 Hz was found to be more significant in terms of vibration. It was also found that low-frequency indoor noise levels varied by as much as 20dB with position in a room, due to the existence of room resonances.