Experimental Response of Condenser Microphones Under Hyperbaric Conditions

Acoustic phenomena of practical interest typically take place either in air at sea level, high altitude, or underwater. Accordingly, devices such as microphones and hydrophones have been developed to accurately measure sound in these conditions. In air at elevated pressures, typical condenser microphones should continue to operate, though the details of their performance are not readily available. Characterizing the response of microphones at high pressure will allow for a new regime of experimental aeroacoustics to be explored, including upcoming work which utilizes small model rotor blades in hyperbaric conditions to achieve aerodynamic scale similarity with full-size rotorcraft. To evaluate the response of condenser microphones in high pressure air, a pistonphone calibrator was developed to provide known reference signals over a wide range of ambient pressures and frequencies. The design of the pistonphone calibrator will be outlined and methods presented for evaluating the response of typical condenser microphones over a range of frequencies and elevated pressures up to 100 bar.