The effects of high-frequency natural sounds on ambient monitoring in Massachusetts

Natural sounds produced by insects, frogs and birds can significantly affect the results of environmental ambient sound monitoring programs, particularly those conducted in Massachusetts during the warmer seasons when those creatures are most active. In fact, the effects of ambient temperatures on the frequency of cricket chirps can be traced back to an article published in 1897, commonly known as “Dolbear’s Law”. More recently and relevant to this paper, INTER-NOISE 2010 included a paper that lead to a 2014 ANSI/ASA standard which included a method for filtering out the effects of high-frequency natural sounds (HFNS) from measured sound levels. We have found that applying this filtering approach for long-term ambient monitoring programs can significantly reduce the presumed ambient sound level by as much as 15 A-weighted decibels. This can lead to a lower impact threshold for sound compliance, and potentially additional noise controls and costs for a proposed project. This paper will present the results of recent environmental ambient sound monitoring programs conducted for permitting in quiet suburban Massachusetts that included high-frequency natural sounds, along with an analysis of the ANSI/ASA standard for filtering out the effects of those sounds and a comparison of other creative filtering methods.