Noise Exposure Dose Research Articles

Industrial warning signal detection under augmented hearing protection devices

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.]

Do Amplitude-Sensitive Hearing Protectors Improve Detectability of Vehicle Backup Alarms in Noise?

Signal detection thresholds to a vehicle backup alarm were determined for audiometrically-normal subjects under broadband (pink) noise at 75, 85, and 95 dBA. The objective was to compare detection performance achieved under two contemporary amplitude-sensitive hearing protection devices (HPDs), an electronic Peltor T7-SR earmuff and a passive, orifice-type E-A-R Ultra 9000 earmuff, against detection achieved under the conventional (non-amplitude-sensitive) counterparts to these muffs, a Peltor H7A and an E-A-R 2000. Amplitude-sensitive HPDs are intended to provide better hearing in low noise levels either through band-limited amplification of outside sounds (electronic Peltor muff), or through reduced attenuation via passage of low-intensity sounds (E-A-R 9000). However, for the noise conditions and common warning signal tested, the amplitude-sensitive HPDs produced no statistically-significant advantage in masked signal threshold compared to the conventional muffs. Therefore, it cannot be concluded that these amplitude-sensitive muffs will improve aural detection of important workplace sounds of similar frequency content to the backup alarm evaluated herein. A separate analysis comparing the dBA levels experienced under the Peltor electronic muff with the circuit on and off indicated that the subjects’ gain control setting did not significantly increase the noise exposure dose over amplifier-off conditions.