Industrial warning signal detection under augmented hearing protection devices

Abstract

The results from several experiments concerning the effects of passive, Amplitude-Sensitive Sound Transmission (ASST), and Active Noise Reduction (ANR) HPDs on vehicle backup alarm detection by normal hearers are reviewed. Masked thresholds under a Peltor electronic ASST earmuff and an AEARO orifice-based ASST earmuff were found not to differ significantly from thresholds under conventional earmuffs of similar volume to the ASST devices, in pink noise of 75, 85, and 95 dBA. A separate analysis using a KEMAR manikin indicated that subjects’ chosen settings of the Peltor ASST earmuff gain control did not significantly increase the noise exposure dose over the earmuff’s amplifier-off setting. In low frequency-biased ‘‘red’’ noise conditions (averaged across 85 and 100 dBA), masked thresholds under a Bose ANR earmuff and an AEARO foam earplug were significantly lower (better) than those under a Peltor passive earmuff having weaker low frequency attenuation, but there were no differences among the 3 devices in pink noise, nor at 85 dBA in either noise. Detection thresholds in 85 dBA noise were 3.2–4.5 dB lower in the 3 protected conditions than in the unprotected condition, attesting to the fact that HPD use can facilitate signal detection under certain conditions for normal hearers. [Work supported by U.S. Bureau of Mines (now NIOSH), Bose Corp., Aearo Corp.]