Reciprocity Calibration of Microphones under High Ambient Pressures
Medical research progress rept. no. 5
NAVAL SUBMARINE MEDICAL RESEARCH LAB GROTON CT
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The purpose of this study was to demonstrate a technique for primary calibration of microphones under high ambient pressures and various gas mixtures. The reciprocity calibration technique was chosen for calibrating a piezoelectric microphone to 600 feet in a helium-gas mixture and depth changes were applied to the basic reciprocity formula. Using the reciprocity calibration technique with a piezoelectric microphone it was found that sensitivity decreased at frequencies below 2000 Hertz as pressure increased. At the pressures encountered from 300-600 feet, the sensitivity of the microphone was stable from 3000 to 8000 Hertz. Between the surface and 600 feet depths, there was approximately a 15 to 18 dB loss in sensitivity.