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Effect of the M25 Protective Mask and Hood on Speech Intelligibility and Voice Level.
HUMAN ENGINEERING LAB ABERDEEN PROVING GROUND MD
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The speech intelligibility of the M25 protective mask and hood was evaluated outdoors at distances of 1, 4, 16, and 32 meters. Computed intelligibility obtained without the use of the protective mask was compared to these results. Voice level measurements and spectral analyses were made using two different measures of voice level articulation index computations were also performed. The subjects rated difficulty of communicating at each distance and estimated the maximum effective communication distance. When wearing the M25 protective mask and hood, speech intelligibility does not meet normally acceptable requirements even at 1 meter, and meets minimally acceptable requirements only at distances of up to a maximum of 12.5 meters. Mean phonetically balanced PB word intelligibility when wearing the protective mask and hood ranged from 70 percent at 1 meter to 20 percent at 32 meters intelligibility computed for a no-mask condition ranged from 97 percent to 56 percent for the same distances. Based upon the intelligibility requirements of MIL-STD-1472C DoD, 1981, the maximum distance at which minimum effective communication could take place with the protective mask and hood was 12.5 meters. The subjects ratings of communication difficulty were similar to the objective results.
APPROVED FOR PUBLIC RELEASE