Measurement of Sound in Airflow
The suitability of a number of different microphone configurations for making sound measurements in airflow was assessed. When a microphone is immersed in airflow, turbulence within the airflow interacts with the diaphragm causing the microphone to measure a noise level, which is due to the turbulence/diaphragm interaction and is not due to an acoustic wave. This turbulence-induced 'pseudo-noise' is equivalent to background noise and can interfere with sound level measurements if the pseudo-noise level is similar to the level of sound being measured. Instances where pseudo-noise may be a problem include measurements made out-doors where the microphone is subjected to atmospheric wind or measurements made in wind tunnels or HVAC ducts. In this paper a number of different microphones and microphone treatments were investigated for their suitability for minimizing pseudo-noise.