Response Variations of Three Types of Microphones Pressurized to 19 ATA
Interim rept. no. 8
NAVAL SUBMARINE MEDICAL RESEARCH LAB GROTON CT
Pagination or Media Count:
The purpose of the study was to determine what changes three types of microphones undergo during compression and decompression to 19 ATA equiv. to 600 feet of sea water, using a mixture of helium and oxygen. A reciprocity calibrated ceramic microphone was used as the standard for observing the changes of a cardioid ribbon type condenser microphone. The results indicate that sensitivity of all microphones decreases as ambient pressure increases. In addition, there are substantial changes in the linearity of the transducers especially at frequencies above 3000 Hertz. The ceramic microphone demonstrated the most consistent responses during descent and ascent. At 17 hours post-dive, it also showed a frequency response that was within one dB of the pre-dive values at all frequencies tested. From this investigation, it would appear that none of the three types of microphones is ideally suited for speech communication in helium-oxygen environments due to the roll off in sensitivity at the high frequencies at depths greater than 200 feet.
- Voice Communications