Audiometer and Equipment Calibration and Biological Checks
Three levels of assurance
Audiometric equipment is checked at three levels. First, a functional or listening check each day before testing: listen to each earphone, sweep the attenuator, flex the cords, and listen for static, distortion, or a silent channel. Second, a biological check - test one or more people with stable hearing and compare results to their stored reference audiogram. Third, electroacoustic calibration by a certified laboratory at least annually and after any repair, service, or relocation, performed to ANSI S3.6.
The biologic check is the practical defense against drift. Common practice allows ±10 dB at each frequency; a larger difference triggers investigation and, if confirmed, recalibration. Keep reference audiograms and the check log with the audiometer. The acoustical calibrator used to check sound level meters and dosimeters is itself sent out for calibration on a regular cycle.
Traps
Questions frequently swap the daily listening check with the annual electroacoustic calibration. Another favorite: the standard's calibration tolerance (typically ±3 dB for audiometer output) versus the ±10 dB tolerance applied to the biologic check. Do not assume a new audiometer arrives calibrated, and remember calibration is also required after repair, not just annually.
Rule of thumb: listen daily, calibrate annually, recalibrate after any repair - and document all three.