Abstract :
The major problems of underwater communication are microphone and earphone construction speech distortion caused by high pressure and/or mixed gas breathing environments, and face mask design. Microphone and earphone elements have recently been developed that are relatively unaffected by increased ambient pressure. These elements are constructed of piezoelectric ceramics encased in a unique rubber housing to prevent water leakage. Preliminary tests indicate that the frequency response of these elements is changed less than 3 dB by pressures exceeding 500 lbf/in2gauge. Extensive research in speech distortion under extreme pressures with various gas mixtures includes voice spectrum analysis, study of adaptation changes in speech, and intelligibility measurements of helium speech before and after processing or "unscrambling." These basic data provide information for the design of microphones, masks, and electronic and mechanical means of normalizing distorted speech. Face mask design must include consideration of breathing requirements, as well as speaking requirements. The design of a speaking cavity has, of necessity, been based on empirical data. These designs often conflict with the primary requisite of proper breathing design. Electronic compensation is often employed to correct or improve deficiencies in mask characteristics.
