SOUND ATTENUATION CHARACTERISTICS OF THE PROJECT MERCURY PRE-PRODUCTION FULL PRESSURE SUIT HELMET

To determine the sound attenuation characteristics of the Project Mercury preproduction full pressure suit helmet using two different methods: (1) Psychophysical: The differences between a trained listener's auditory thresholds for various test tones without helmet and the thresholds obtained while wearing the helmet defined the relative attenuation values at low sound pressure values. (2) Physical: Differences between sound pressures measured outside the suit and those measured under the right earphone cushion by a probe microphone were taken as attenuation values under high sound pressure level (SPL) conditions. Measurements made under low SPL conditions show that the 'real-ear' attenuation values obtained with test tones 250 cps, 500 cps, 4000 cps, 6000 cps, and 8000 cps exceeded pre-established specifications. Attenuation values obtained with test tones 125 cps, 1000 cps, 2000 cps, 3000 cps, and a wide band of noise (20 to 10,000 cps) did not meet specifications. The attenuation measured by physical methods using as reference frequencies 125 cps, 500 cps, 1000 cps, 2000 cps, 3000 cps, 4000 cps, 6000 cps, and 8000 cps each presented at 120 db sound pressure levels did not meet specifications. (Author)