Hearing thresholds, threshold repeatability, and attenuation values for passive noise-reducing earphone enclosures.

Passive noise-reducing earphone enclosures contain a supra-aural earphone mounted in a plastic dome. These enclosures are used to prevent the elevation of hearing thresholds due to masking from high levels of ambient noise. This research determined normal hearing threshold levels, threshold repeatability, and attenuation values for an Audiocup, Auraldome II, AudioMate, and Madsen ME-70 enclosure. In Study I hearing thresholds were obtained for 30 normally hearing adults from 500 to 6000 Hz in four test sessions for each enclosure and a supra-aural earphone attached to a headband. The hearing thresholds and repeatability for the Audiocup and Auraldome were similar but the thresholds were higher and repeatability was poorer for the AudioMate and Madsen ME-70 compared with the supra-aural earphone. In Study II real-ear attenuation values were obtained for each enclosure using 24 normally hearing subjects. The Audiocup and Auraldome II provided less low-frequency attenuation compared with the AudioMate and Madsen ME-70. The findings were related to the coupling of the supra-aural earphone in each enclosure to the ear and the coupling of each enclosure to the head. If an enclosure is used as an alternative to a supra-aural earphone for hearing testing in high ambient noise environments, hearing thresholds and threshold repeatability should be similar to a supra-aural earphone, and the enclosures should provide adequate attenuation of ambient noise. Since none of the enclosures met all of these requirements their use is not recommended for hearing testing.