Aeroacoustic probe design for microphone to reduce flow-induced self-noise

A new aerodynamic microphone forebody design was tested in the National Full-scale Aerodynamics Complex (NFAC) at NASA Ames Research Center. An overview of the design theory is presented. The new microphone forebody was tested along with the industry standard Bruel and Kjaer (B&K) aerodynamic microphone forebody in the Ames 7- by 10-Foot Wind Tunnel, NFAC 40- by 80-Foot Wind Tunnel and Anechoic Chamber. The wind tunnel results show that high frequency tones, present with the B&K microphone forebody, are eliminated with the new probe. Broad band background noise levels at lower frequencies are also shown to decrease with the 1/4 inch version of the new probe. Finally, the Anechoic Chamber results show no difference in the directional characteristics between the new and B&K microphone forebodies below 80 kHz.