Real ear attenuation at threshold for three audiometric headphone devices: implications for maximum permissible ambient noise level standards.

Attenuation measurements were made using the ANSI S12.6-1984 protocol on a standard Telephonics headset with TDH-50P earphones and Model 51 cushions, Amplivox Audiocups headphone enclosures, and Peltor AudioMate headphone enclosures. Each of the enclosures housed Telephonics TDH-50P earphones with Model 51 cushions. The mean attenuation values obtained were compared with those previously reported, and reasons for discrepancies were analyzed. Pure-tone threshold shifts in background noise complying with ANSI S3.1-1977 and Occupational Safety and Health Administration (1983) maximum permissible ambient noise level standards were estimated on the basis of the attenuation values for each headphone device, and the adequacy of these current standards for accurate pure-tone threshold assessment was considered. The results indicated that Model 51 cushions alone are insufficient to attenuate the ambient noise levels permitted under ANSI S3.1-1977, and even the utilization of noise-excluding headphone enclosures does not reduce the background noise levels permitted under the Occupational Safety and Health Administration (1983) to a sufficient degree to permit testing down to 0 dB HL.