Equivalent hearing threshold levels for the Etymotic Research ER-10C otoacoustic emission probe

To determine the equivalent threshold sound pressure levels (ETSPL) for a commercially available distortion product otoacoustic emission (DPOAE) probe, and to study the impact of probe fitting and eartip size on the calibration.

Twenty-eight otologically normal test subjects participated in the ETSPL determination for the Etymotic Research ER-10C probe.

ETSPLs were determined up to 16 kHz and were compared to the reference hearing thresholds associated with the ER-3A insert earphone. Both 'regular' and 'baby' foam eartips were used.

At most frequencies, no significant threshold differences were observed between the insert earphone and the DPOAE probe. However, at 1 kHz and 4 kHz, the mean thresholds for the insert earphone were generally lower than those for the DPOAE probe, suggesting systematic differences at those frequencies. Repeated calibration runs resulted in deviations of about 0.6 dB. Similar deviations were noticed when using foam eartips of different sizes up to 10 kHz.

Knowing the reference thresholds for DPOAE probes enables measurements of (subjective) hearing thresholds and (objective) otoacoustic emissions using the same probe. Probe fitting and eartip size had negligible effect on the determination of ETSPLs. The obtained data may be proposed for inclusion in future audiometry standards.