Wind-induced noise in a screened microphone

To reduce the effect of wind on a microphone, wind screens are used, usually made of foam or cloth. Although this measure to reduce wind noise is well known and widely used, it lacks a theoretical explanation. One possible explanation was the turbulent wake in the air flow behind the wind screen, another the pressure variations due to turbulence inherent in outdoor wind. In the present paper it is shown that atmospheric turbulence is indeed the cause of outdoor microphone wind noise, and the knowledge that is available in atmospheric boundary layer physics can be used to model the effects of atmospheric turbulence on a bare or screened microphone. A wind screen can be seen as a first order low pass filter for pressure variations due to atmospheric turbulence. Induced wind noise is thus determined by (average) wind speed and wind screen diameter, but also by factors related to frictional and thermal turbulence (roughness length and atmospheric stability). This approach leads to predicted spectral values of the induced "sound" pressure that match experimental data. The result can be used to obtain proper outdoor ambient wind related sound levels by correcting measured sound levels with calculated wind-induced pressure levels. (c) 2006 Acoustical Society of America.