Flow induced noise reduction techniques for microphones

Wind tunnel noise measurements are a common application in the aerospace and automotive industries. The measured sound pressure levels from microphones are affected greatly by the presence of air flow across the microphone diaphragm in these cases. The dynamic pressure field measured by the microphone includes both the acoustic pressure and the pressure induced by the air flow. There are three types of microphone accessories that are commonly used to perform wind noise isolation: gridcaps, windscreens, and nose-cones. In this study, each of these microphone accessories is tested in a wind tunnel using 1/4 inch and 1/2 inch microphones in turbulent and laminar flows at flow speeds up to 55 mph and in both head-on and parallel diaphragm orientations. Two types of flush mount microphones, a surface mount and a side-vented pressure microphone, are also evaluated. The effects of background flow noise on the microphone measurements is shown for all conditions and a case study is presented with an arbitrary acoustic source. Finally, recommendations are presented for which accessories are best used in different measurement situations.