Cooper, S. Measurement of Infrasound & Low Frequency Noise for Wind Farms (Amended Version), Denver 2013
Steven Cooper, The Acoustic Group Pty. Ltd.
5th International Conference on Wind Turbine Noise, Denver 28-30 August, 2013
This amended version of the original paper is different to that contained in the conference proceedings following advice that errors in the original paper concerning the Z weighting of the 1/3 octave bands in the SVAN 957. The author in the presentation acknowledged the error and gave an undertaking to those present to re-issue the paper. There follows part of the Conclusion to the Amended Paper.
The concept of utilising dB(G) to describe infrasound levels associated with wind turbines at residential receivers has a fundamental flaw due to the definition of the G-weighting curve which can be obtained by reference back to International Standard ISO 7196:1995.
Due to the specific frequency weighting characteristics of the G function, whilst the proportion of energy below 6.3Hz is evident in a linear format for such measurements, such energy is not reflected in the dB(G) value.
The relevance of use dB(G) to determine the human perception of infrasound from turbines has not been established or whether in fact the suggestion of a hearing threshold based on dB(G) is appropriate for turbine noise.
There is danger in utilising or presenting material as Linear levels when using instrumentation that has a dB(Z) weighting that may have different frequency responses below 5Hz and potentially different compensation filters that need to be identified.
Not all meters have the same dB(Z) filter or even true Linear spectrum results, nor do most consultants or calibration facilities have the ability to calibrate complete systems across the full infrasound spectrum.