Acoustic Ranging Technique for Assessing Low-Frequency Acoustic Noise from Wind Turbines

Abstract

An acoustic source ranging procedure is obviously a research tool and would not normally be attempted by an individual wind turbine owner. The minimum equipment necessary for the analysis includes three microphone systems preferably with very low-frequency response, an FFT dual-channel signal analyzer with hard copy or data output capability, and the necessary cabling. There is no requirement to record the acoustic data although it is certainly easier to post-process the data when all three microphone pairings can be analyzed from the same time record. If this is done, a suitable FM tape recorder with at least three tracks is required.

Assessment of the degree of concentration of source region within a swept area is necessarily somewhat subjective. The time signal itself from one microphone should also be examined for periodic impulsiveness which would indicate a localization of source region. This can be analyzed in parallel with blade position (abiding acoustic transport delays) to corroborate a source ranging location.