HUMAN FACTORS, 1990,32(1),9-25 Attenuation Performance of Four Hearing Protectors under Dynamic Movement and Differen t User Fitting Conditions

An experiment was conducted to determine the effects of movement activities and alternative fitting procedures on protection levels afforded by four hearing pro-tection devices (HPDs). Psychophysical attenuation measurements at nine one-third-octave bands from 125 to 8000 Hz were obtained prior to, during, and fol-lowing a 2-hr wearing stint that included periods of either highly kinematic but controlled work activity or vigorous temporomandibular movement. The 40 sub-jects, who were nonusers of HPDs, initially fit the protectors according to either the instructions on the package (i.e., subject fit) or after receiving interactive train-ing on proper fit (i.e., trained fit). Thereafter no further protector adjustments were allowed during the wearing period. The subject-fit condition resulted in signifi-cantly lower protection levels, from 4 to 14 dB, at 1000 Hz and below for a pre-molded polymer earplug, a user-molded foam earplug, and a double protector consisting of a muff over the foam plug. The muff alone was significantly more resilient to fitting effects on attenuation than were the plugs. Movement activity caused up to a 6-dB significant reduction in frequency-specific attenuation over time for the premolded plug, muff, and muff-plug combination. The compliant foam earplug was largely resistant to either type of movement effect but did ben-efit more than the other devices from use of the trained-fit procedure. Implications of the results for hearing protector testing protocol, device selection, and user training are discussed