Calibration matters: II. Measurement of ambient noise in test rooms/areas

Ambient noise measurement is a part of audiometric calibration in which one measures the ambient noise level in a sound room/test area intended for audiometric testing and then decides whether the background noise in the test room meets the maximum permissible ambient noise level (MPANL) requirements specified in national or international standards, e.g., ANSI/ASA S3.1:1999(R2018) or ISO 8253-1:2010 (R2021). If the ambient noise levels are below the MPANLs, clinicians can be sure that the test stimuli they present to patients are not masked by the background noise in the test room/area and their test results are valid and the subsequent clinical decisions are sound. Audiometric testing, however, may not always be carried out in sound rooms/test areas with ambient noise levels below the MPANLs, especially during community outreach or humanitarian services. A thorough understanding on the MPANL requirements for different transducers can help clinicians determine which equipment is appropriate for the test area. This tutorial discusses the rationale and assumptions behind the MPANL specifications, how to measure ambient noise levels of test rooms/areas, and how to apply the national and international standards to determine if the test room is suitable for audiometric testing. Alternative strategies are discussed when the ambient noise levels exceed the specified MPANLs. The rationale and procedures are explained using examples on how to lower the ambient noise levels in test areas, and how to determine the suitable test frequency range and the lowest threshold levels that can be assessed in the test area.