Active noise reduction versus conventional hearing protection. Relative benefits for normal-hearing and impaired listeners.

The benefits of active noise reduction (ANR) hearing protectors were assessed in two groups of normal-hearing subjects, under and over the age of 40 years, and one group with bilateral high-tone hearing loss. Subjects were tested with the ears unoccluded and fitted with conventional sound attenuating E-A-R foam plugs, E-A-R HI-FI plugs, and Bilsom Viking muffs; and one ANR muff, the Peltor 7004. Within each ear condition, measurements were made in quiet of hearing thresholds for frequencies between 0.25 kHz and 8 kHz, duration and frequency difference limens, and word recognition. Hearing thresholds and word recognition were also measured in a background of impulsive cable swager noise. The E-A-R foam plug provided the highest and the E-A-R HI-FI plug, the lowest attenuation. The Bilsom Viking and Peltor muffs were virtually identical and midway between. An additional 10 dB of sound reduction was realized at 0.25 kHz with ANR. The masking effect of the noise on hearing threshold decreased with an increase in attenuation. None of the devices compromised either duration or frequency discrimination. Word recognition in noise improved in normal listeners when protectors were worn. For the impaired subjects, word recognition with poor contextual cues decreased with an increase in sound attenuation, in both quiet and noise. Like older normal listeners, their scores were relatively higher with ANR.