Laboratory performance of the single-sided E-A-R® combat arms hearing protective earplug
Keywords:Acoustic generators, White noise, Centre frequency, Error types, Hearing loss, Hearing protection, Hearing threshold, Horizontal planes, Key factors, Laboratory performance, Mode of operations, Modes of operation, Noise bands, Normal hearing, Sound attenuation, Sound source identification
AbstractThe objective of this study was to compare the effect of wearing conventional and passive level-dependent hearing protection earplugs on hearing and horizontal plane sound source identification, in quiet. A single device was tested that incorporated these as separate modes of operation. Ten males and ten females with normal hearing participated. Each was tested with the ears unoccluded and fitted binaurally with the device in each mode. Measurements were made of free-field hearing thresholds for one-third octave noise bands with centre frequencies ranging from 250 Hz to 8000 Hz and the ability to discriminate among eight speakers surrounding the subject at a distance of 1 metre. The stimulus was a 300-ms, 75-dB SPL white noise burst. The sound attenuation was derived from the hearing thresholds. With the device in the conventional mode, mean thresholds were in the range of 36.2 dB to 53.3 dB SPL, signifying an induced mild hearing loss. In the level-dependent mode, thresholds were at most 37.9 dB SPL. Mean attenuation values were generally similar to the manufacturer's specifications. There was no effect of gender. Percent correct for sound source identification decreased by 40% with the conventional mode and by 20% with the level-dependent mode. Degree of attention, then appears to be a key factor for outcome. However, an analysis of error types showed that the level-dependent mode of operation resulted in a frontward bias that was similar to that observed previously with a device incorporating external microphones for enhanced communication.
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