Microphone design and selection for deep-submergence environments

The acoustic impedance and velocity of sound are increased considerably in the deep-submergence hyperbaric HeO gas mixture. This increases the spectrum bandwidth of speech and at the same time alters the frequency response of microphones designed for use on the surface. The mechanical elements of microphones are not affected by gas composition and pressure; however, the acoustical elements are affected non-proportionally. Thus, a microphone which is carefully tuned at one atmosphere in air may be considerably out of adjustment under hyperbaric conditions. The problem of finding a conventional microphone to meet specialized requirements can be alleviated by designing for hyperbaric conditions. Systems with a high mechanical impedance will not be affected by gas composition and pressure. Effective waterproofing is essential. For applications in masks, noise-cancelling microphones are very effective.