scope:

Hearing measurements in an audiometric test room may be conducted for different audiometric purposes over different test frequency ranges. However, if the ambient noise level is excessively high, some hearing threshold levels measured in that environment will be inaccurate. This occurs because excessively high ambient noise will create an elevation of hearing threshold levels. This is a psychoacoustic phenomenon called masking.

Exclusion of all ambient noise from an audiometric test room is not feasible nor practical from structural and cost considerations. However, to ensure that hearing tests are not influenced by excessive ambient noise masking, there is a need to specify maximum permissible ambient noise levels (MPANLs) that can be allowed in an audiometric test room. This is true particularly when testing is done at sound pressure levels for pure tones corresponding to 0 dB hearing level. Further, there is a need to specify MPANLs for different audiometric conditions, test frequency ranges, and earphone types that will permit testing at reference equivalent threshold levels specified in ANSI S3.6- 1996 American National Standard Specification for Audiometers.

This Standard includes the specification and measurement of MPANLs in an audiometric test room. Within this Standard, MPANLs are specified for octave and one-third octave band intervals from 125 to 8000 Hz for the audiometric conditions of testing with ears covered using a supra-aural and insert earphone and ears not covered for the test frequency ranges 125 to 8000 Hz, 250 to 8000 Hz, and 500 to 8000 Hz.

Purpose

The purpose of this Standard is to specify MPANLs in an audiometric test room and measurement procedures that will produce negligible masking (<2 dB) of pure tones presented at reference equivalent threshold levels as specified in ANSI S3.6-1996 American National Standard Specifications for Audiometers for different audiometric conditions and test frequency ranges.

This Standard is intended for use by all persons conducting hearing tests to ensure that ambient noise in an audiometric test room will not have a masking effect or influence on hearing measurements. This Standard is also intended for distributors, installers, designers, and manufacturers so that they can plan and construct appropriate acoustical treatment for the reduction of ambient noise in audiometric test rooms.