Speech understanding in noise with earplugs and muffs in combination

An experiment was conducted to determine the effect on speech understanding of an earplug and muff, worn in combination. Two groups of 12 normal-hearing subjects were tested individually in a semi-reverberant chamber. The measurements included free-field assessment of hearing thresholds from 0.25 to g kHz and consonant discrimination, with the ears unoccluded or fitted with E-A-R foam plugs, the Peltor Aviation communication headset, or the two devices in combination. The headset had active noise reduction (ANR) capability, and was tested without and with ANR operational. The speech was presented at a level of 85 dB SPL either in speech spectrum noise (Group 1) or cable swager noise (Group 2), presented with speech-to-noise ratios ranging from +5 to -10 dB. The two noise backgrounds differed in terms of both energy spectrum and temporal characteristics. The results showed that below 2 kHz, the devices worn in combination provided as much as 30 dB more sound attenuation than either device alone. The effect of the combination on consonant discrimination was a decrease of only 4%. The type of noise background and speech-to-noise ratio proved to be more important determinants of outcome. (C) 1998 Elsevier Science Ltd. All rights reserved.