Abstract
Unusual breathing environments such as those containing helium are being considered for future manned space systems. In the study reported herein, the physical acoustic characteristics of speech generation were investigated for helium concentrations of 0%–70% at pressures from sea level to 258 mm Hg. An electromechanical-acoustical model of the vocal tract for the sustained phonetic vowel sounds of [i] (eat), [o] (lost), and [u] (boot) was utilized to determine the shift in formant frequency and the change in acoustic power radiated relative to that for normal air. For comparison purposes, the relative acoustic powers were calculated for the sss and th fricatives, some simple ideal acoustic generators and moving voice coil-type loudspeakers; in addition, loudspeaker directivity characteristics and power output were experimentally measured. Previously noted impaired communication capability in these environments can be attributed to speech spectrum changes due to the nonuniform power reduction of vowels and consonants and changes in formant frequency and directivity.
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