An evaluation was made as to the tone, noise, and speech threshold attenuation characteristics of the Gentex RCA X-l and the RCA X-2 personnel noise protective devices, each tested with a liquid ear cushion and a foam rubber ear cushion. Two genera! types of measures were obtained;1) physical measures taken from the output of a miniature condenser microphone serving as an artificial ear mounted within a plaster manikin head;and 2) listener-observer judgments of threshold shift, normal listening versus device over the ears, to the various stimuli presented ambiently to 10 individuals. The judgments included responses to: a) pulsed pure tone at eight discrete frequencies, b) pulsed wide-band and octave-bands of noise, and c) Spondee
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