Consequences of the change to standards for air-conduction hearing levels. A cautionary note

The issue of BS 2497 Parts 5 and 6 in 1988 brought British Standards into line with the latest revisions to ISO 389. As a consequence, many audiometers that were previously calibrated using a 9-A coupler will now have to be calibrated with an artificial ear. Whilst this may appear to be a seemless change involving merely alterations to measurement apparatus, this technical note illustrates for two earphone types that it entails a shift in the Hearing Level standard by a maximum of 3 dB at 2 kHz. This has ramifications for longitudinal studies of hearing and for monitoring of hearing threshold levels in persons exposed to noise.