Sound localization with hearing protectors.

A preliminary investigation was conducted of the ability of normal-hearing subjects to localize sound while wearing hearing protective devices. Performance with Bilsom 2392 level-dependent stereophonic muffs with limited amplification was compared with that of conventional level-independent E-A-R 3000 muffs and E-A-R plugs. Sound localization was assessed using an array of six speakers, positioned in the horizontal plane, 1 m from the subject at azimuth angles of 30 degrees, 90 degrees, 150 degrees, 210 degrees, 270 degrees and 330 degrees. The stimulus was an 80 dB SPL 300-ms one-third octave noise band centered at 500 Hz or 4000 Hz. The experiment was conducted in quiet and in a 65 dB SPL white noise background. The results indicated that at 500 Hz, the wearing of protectors resulted in a 20% decrease in the accuracy of speaker identification but the three types of device were indistinguishable. At 4000 Hz, performance was best in the unoccluded condition and relatively worst with the level-dependent muff. Error patterns depended on the interaction of stimulus frequency, speaker azimuth and protector. Front/back errors in localizing the high-frequency stimulus were greatest with the conventional muff, whereas right/left errors were greatest with the level-dependent muff. Protected listening was generally unaffected by the presence of a noise background for both of the frequencies tested.