Calibration and uncertainty evaluation of the devices for audiometry

The devices for audiometry such as audiometer, ear simulator, and mechanical coupler are listed in the BIPM service category and should be calibrated in principle. The international standards for these devices have been well established however the concept of uncertainty is not widely adopted to the audiologists in the field. From this reason, the uncertainty of audiometry has not been precisely evaluated and overestimated. An example of the uncertainty evaluation in audiometry to determine the hearing threshold level is presented based on the permissible deviated levels of each component in the ISO 8253-1: Annex A. The presented value in this example is 10 - 14 dB for air conduction and 11 - 15 dB for bone conduction. These are quite large values concerning the resolution of audiometer, 5 dB in general. Therefore, it is essential to reflect the exact uncertainty value for each related device. In this study, the methods of traceable calibration are applied to calibrate the ear simulator and the related uncertainty evaluation is conducted for each step of traceability chain. Based on the calibrated ear simulator and coupler, the measurement uncertainty of audiometric test can be significantly reduced in comparison with the value estimated with the permissible deviations.