An investigation of the sources and attenuation of wind noise in measurement microphones

A theoretical and experimental study of wind noise in unscreened and windscreened microphones was undertaken to achieve three objectives. They were: to determine the primary sources of wind noise outdoors; to determine the mechanism for wind noise reduction by windscreens; and to investigate the frequency dependent relationship between a local velocity measurement and the microphone signal. Results indicate that the main sources of wind noise for an unscreened microphone are pressure fluctuations caused by shears in the mean and fluctuation velocities in turbulent eddies around the microphone and a local fluctuation near the boundary layer of the microphone diaphragm where the shear in the mean velocity is very large. The volume fluctuations in the flow put a limit on the correlations between a local velocity measurement and a corresponding wind noise measurement and, thus, limit the potential for signal processing between a hot-film anemometer probe and a microphone. In a windscreened microphone, the local fluctuation is removed and what remains is a pressure distribution on the surface of the windscreen that is a result of eddy convection by the windscreen. Eddies that are much larger than the windscreen contribute the most significant amount of wind noise at frequencies below 10 Hz for the windscreens tested.