Background noise in rooms used for pure-tone audiometry in disability assessment.

Background noise limits for audiometry are determined by the effects of masking and are specified in international standards. The standards provide for audiometric testing over a range of audiometric frequencies extending down to 500 Hz or lower. The lowest frequency of testing is an important factor determining the admissible noise, and for certain applications it is appropriate to consider the limits applicable to testing over a more restricted range. Assessment of hearing disability in the UK is generally based on a consideration of pure-tone hearing threshold levels in the frequency range 1 kHz upwards. A modification of the standardized noise limits is proposed which allows some relaxation appropriate to this higher minimum frequency. For air-conduction audiometry, these modifications affect only the permissible background noise in the frequency range below 1 kHz. Where bone-conduction audiometry is required in order to quantify a conductive component of the hearing loss, the measurements need to be made on both ears with the non-test ear masked in both cases; the external background noise will thus only be heard monaurally and this justifies a correction to the noise limits compared with those appropriate to bone-conduction audiometry without masking.