Abstract
Differences in signal tone perception between 1 atm (14.7 psia) and 13 atm (5.0 psia) in the presence of background noise were investigated. In addition to the generation of a background noise spectrum conforming to that specified for spacecraft of the Skylab program (NC 55 approximately), predicted acoustic properties of the spacecraft were simulated. SPLs of three signal tones were experimentally varied using the “Block Up-and-Down, Two-Interval Forced-Choice” technique. Masked thresholds were determined for the three signal tones under the two air pressure conditions and compared with predicted masked thresholds and subjective preferences. The data indicate that the difference in ambient pressure between 14.7 and 5.0 psia does not significantly affect masked thresholds, nor does this difference in ambient pressure affect subjective preferences for signal tone SPLs or sound quality. A further finding indicated that reduced pressure significantly affected the SPL of sound producing equipment in that the SPL decreased with a decrease in pressure but not in accordance with the expected formula 10 log10(ρc/ρ0c0). [This study was supported by a NASA contract.]
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