An experiment was conducted to study earmuff wearers’ signal detection in noise performance and perceptions of comfort and acceptability with two amplitude-sensitive earmuffs as compared to their conventional counterparts. Passive and electronic amplitude-sensitive earmuffs were tested, represented by the EAR Ultra 9000 and the Peltor T7-SR, respectively. Directly comparable earmuffs, the EAR 2000 and Peltor H7A, were used as conventional controls. The effect of the Peltor T7-SR’s gain on noise exposure and the attenuation of all earmuffs was also assessed. Signal detection performance was assessed via masked threshold determination in three levels of pink noise (75, 85, and 95 dBA), using a digitized back-up alarm as the detection stimulus. A modified Hughson-Westlake procedure was used to obtain 10 trials for each earmuff under each noise level. Comfort and acceptability were investigated via questionnaire. Real-ear-at-threshold (REAT) attenuation measures were recorded at 500 and 1000 Hz to ensure consistent earmuff fitting and measurements were made of the effect of subjects’ Peltor T7-SR gain settings in each noise level using a KEMAR manikin. Results indicated that only the noise level significantly influenced subjects mean masked thresholds; masked threshold increased linearly with noise level. The lack of a significant earmuff main effect or interaction could have resulted from the step size used to present the stimulus, the noise type or levels used, or the number of experimental conditions/sessions. No earmuffs were judged significantly different in comfort or acceptability. Noise level and gain status (on vs. off) were found to influence the measures taken on the noise level under the Peltor T7-SR, but the increase in noise dose with the gain control on was small. The estimates of attenuation obtained were reasonable for the devices tested. / Master of Science