Hearing aid coupler output level variability and coupler correction levels for insert earphones.

Area of Science:

• Acoustics
• Audiology
• Metrology

Background:

• Accurate measurement of sound pressure levels (SPLs) is crucial for hearing aid (HA) fitting and performance evaluation.
• Different earphone coupler types exist, potentially leading to variations in SPL measurements.
• Understanding coupler characteristics is essential for consistent and reliable hearing aid testing.

Purpose of the Study:

• To compare sound pressure levels (SPLs) measured using three different hearing aid coupler types: HA-1, HA-2, and DB-0138.
• To assess the stability and repeatability of SPL measurements across different experimenters and repeated trials.
• To investigate the reasons for any observed differences in SPLs between the coupler types, particularly at higher frequencies.

Main Methods:

• Two types of insert earphones (ER-3A and EARTONE 3A) were used for measurements.
• Sound pressure levels (SPLs) were measured using HA-1, HA-2, and DB-0138 configured couplers.
• Independent measurements were conducted by two experimenters over five repeated trials, with and without coupler replacement.

Main Results:

• SPL measurements were highly stable across all experimenters, repeated trials, and coupler types, with variations of +/- 0.2 dB from 125 to 8000 Hz.
• Mean SPLs for HA-1 and HA-2 couplers were similar for each earphone type across the measured frequency range.
• From 3000 to 8000 Hz, the DB-0138 coupler yielded higher SPLs compared to HA-1 and HA-2 couplers due to geometrical differences and acoustic effects.

Conclusions:

• The tested HA coupler types (HA-1, HA-2, DB-0138) demonstrate high measurement stability and repeatability.
• Geometrical differences in earphone-to-coupler connections and coupler design lead to significant SPL variations at higher frequencies (3-8 kHz).
• Observed SPL differences can be attributed to quarter-wave resonances and acoustic horn effects within the coupler systems.