ANSI update: maximum permissible ambient noise levels for audiometric test rooms.

The American National Standards Institute (ANSI) specifies maximum permissible ambient noise levels (MPANLs) allowed in an audiometric test room to ensure that hearing thresholds obtained down to 0-dB HL will not be elevated due to masking by ambient noise. MPANLs were originally specified in 1960 and have been revised in 1977, 1991, and most recently in 1999. The purpose of this report is to offer an overview by providing a historical perspective of the MPANLs recently specified by ANSI (ANSI S3.1--1999), the rationale for revising the MPANLs, the new computational method used for determining the 1999 MPANLs, the ANSI S3.1--1999 octave and one-third octave band MPANLs, and information concerning compliance with the new MPANLs.