Methods for Detecting Low-Frequency Signals in the Presence of Strong Winds.

摘要

This report looks at two methods to better separate blast noise from wind induced noise in unattended monitoring situations. One method is to use a windscreen, a device which prevents wind and wind induced pressures from reaching the microphone diaphragm while allowing the unimpeded passage of true acoustical pressures to the microphone. The second method is to make the microphone-black box system smarter so that it can separate wind induced noise from true blast noise. The results show both methods can do a good job of reducing wind induced noise. For blast noise, where the C-weighted sound is relevant, a special, two-layer wind screen can reduce the C-weighted sound level by almost 30 dB as compared with a bare microphone. Taking the integrated cross product of two vertically spaced microphones (about 60 cm spacing) reduces the C-weighted noise as compared with a bare microphone by about 22 dB. The two methods can be combined, but only when the wind induced noise level is very high and the C-weighted background noise ambient is very low. Otherwise, the two methods together are too good; the maximum useful reduction is the difference between the wind noise level and the background acoustical ambient. Keywords: Blast noise; Wind noise; Monitoring. (jhd)