Comparison of hearing threshold levels using tdh-39 and tdh-49 earphones

Abstract EN

Objective : The study compares hearing threshold levels obtained on the same ear, by using four types of earphones with particular emphasis on the region of 6 kHz, to discover how the differences measured on the coupler translate to measure hearing threshold levels.

Methods : Air conduction audiometry on the same ear of 20 subjects of both sexes using the manual technique was undertaken using four types of earphones, all fitted with MX- 41 / AR cushion using a clinical audiometer type KcSO using 2 dB steps.

Results : The human results are consistent with previous coupler results, showing differences in the order of 6 dB around 6 kHz using international standard methods for calibration; that is using the IEC 303 coupler and associated reference equivalent threshold sound pressure levels for the TDH-39 and the IEC 318 artificial ear for the TDH-49 and TDH-49P.

The source of discrepancy appears to be a specific interaction between the TDH-39 earphone and the IEC 303 coupler. Conclusion : It is concluded that a move away from the use of two different couplers and two different sets of associated reference equivalent threshold sound pressure levels for different earphone types would be beneficial to avoid the problem of differing performance.

Moreover, the IEC 318 artificial ear is recognized as being a better approximation at the human ear than the IEC 303 coupler.