Various problems are encountered during audiometric testing. Deviation from reference threshold levels for supra-aural earphones is often a serious problem when hearing levels are measured. This paper reports the acoustic calibration of clinical audiometers used for special periodic health examination.

ANSI S3.6-1996 Specification for Audiometers represents our most current and best resource for information regarding audiometers. The acoustic calibration was measured in 211 clinical audiometers and compared with the ANSI S3.6-1996 reference threshold levels for supra-aural earphones.

Among 211 clinical audiometers, 56 (26.5%) exceeded the permitted deviation from reference threshold levels at any test frequency in ANSI S3.6-1996 for left supra-aural earphones, and 54 (25.6%) for right. An exhaustive calibration was required for 16 audiometers (7.6%) in both supra-aural earphones. The absolute difference in dB deviation from reference threshold levels by performed acoustic calibration at least annually were statistically significant at any test frequency (p<.05).

The results of this study strongly indicate that clinical audiometry is being conducted with pure-tone audiometers having unallowable sound pressure levels deviations for supra-aural earphones. The validity of audiometric hearing thresholds are significantly affected by these deviations from the acoustic calibration levels of audiometers. Therefore audiometer calibration need to be checked functionally daily and acoustically at least annually.