Bakker et al, Environmental Noise: Better Measures & Reporting Needed
To the layman the measure of environmental sound may seem simple both in terms of measuring the loudness of the sound and determining its annoyance. Nothing could be further from the truth!
H.H.C. Bakker, B.I. Rapley, R. Elliott – Proceeds of ACOUSTICS 2011
In measuring the environmental noise level for such purposes as compliance monitoring and nuisance noise assessment, the most often used statistic is the A-weighted sound pressure level (SPL), often reported as a percent exceedance level (e.g. L10 or L90) averaged over a time interval such as 10 minutes or 24 hours. This statistic can not be relied upon in situations where noise has ‘special audible characteristics,’ such as modulation or tonality, since increases in the sound pressure level (SPL) of the loudest n% of sound will be ignored. Furthermore, the use of Aweighting underestimates the lower-frequency sounds, which have recently been shown to be perceived by humans through alternative mechanisms, therefore different measures are required.
The analysis of large amounts of data for compliance monitoring can be a time-consuming process. Errors can occur due to inappropriate analysis methods or flawed understanding of the noise under investigation. This paper reports on: (1) some of the current issues with using the A-weighting and exceedance statistics as measures of loudness; (2) the development of several alternative measures to analyse environmental sounds from various sources that exhibit ‘special audible characteristics’ (including wind farms and impulsive noise); (3) the requirements of automated, standardised methods of data reporting, analysis and assessment for large and complex data sets and (4) the development of a new sound measurement tool that implements the proposed analysis techniques while extending the acoustic spectrum down to less than 1 Hz: the Spectro-Acoustic Meter (SAM).