Effects of ambient noise masking on earphone thresholds.

Abstract

Monaural thresholds were measured for 24 normally hearing subjects using TDH-49P, Audiocup, and ER-3A earphones from 500 to 6000 Hz in quiet and in background noise having maximum permissible ambient noise levels (MPANLs) specified by OSHA (1983) and ANSI (S3.1-1991). The attenuation for each earphone system was obtained and the actual threshold shift was compared to the predicted threshold shift. The mean threshold shifts were negligible (≤2 dB) in the ANSI MPANLs regardless of earphone and in OSHA MPANLs for the ER-3A but ranged from 2 to 7.5 dB for the Audiocup and from 6 to 12.5 dB for the TDH-49P in the OSHA MPANLs. The results of this study suggest that OSHA MPANLs are too high to allow for testing down to 0-dB HL using these earphones. The high noise-reducing properties of the ER-3A would make it the earphone of choice if testing is done in OSHA MPANLs. Testing down to 0 dB HL can be done in the newly specified ANSI MPANLs regardless of earphone type.