Abstract
Overestimation of hearing protector noise attenuation, as based on laboratory-obtained data, combined with several in-field factors which often degrade protector performance, poses the threat of underprotection for the user. This research investigated the effects of several work-related factors, including wearing time, movement activity, and fitting procedure, on the frequency-specific attenuation achieved with a foam cushion earmuff, two types of earplugs, (slow-recovery foam and flanged polymer), and an earmuff over foam earplug combination. Using a real-ear-attenuation-at-threshold testing procedure, attenuation data were collected from 40 subjects at nine test frequencies. Occluded thresholds were obtained before, during, and after the movement activity task, so that the effects of wearing time and task activity could be determined. The tasks were designed to elicit movements akin to those performed in the typical industrial workplace. The results indicated that achieved attenuation was significantly decreased as a function of time, and that trained-fit provided noticeably greater attenuation than subject-fit without training, though these changes were device-specific. Overall, the study illuminated the strong influence of in-field factors on hearing protector effectiveness, and demonstrated the need for laboratory attenuation tests which yield more realistic results.
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