Probe-Determined Hearing-Aid Gain Compared to Functional and Coupler Gains

In this investigation, hearing-aid gain as measured by a probe-earmold system was compared with gain determined from couplers (HA-2 coupler and ear simulator) and functional-gain measurements. Fifteen subjects with moderate sensorineural hearing loss were tested under aided and unaided conditions in the sound field. In order to determine the effect of the occluded ear canal length on these results, an optical method was developed using an operating microscope to measure the length of the individual subject's occluded ear canal. The results indicate that gain, as measured by the probe-earmold system, corrected for effects of occluded ear canal length, agrees closely with functional and ear-simulator gain through 4.0 kHz. At the frequencies of 5.0 and 6.0 kHz the probe-earmold system underestimated gain particularly when compared to measurements conducted with the ear simulator. Other comparisons were also made between gain measured in a HA-2 coupler and functional gain. The average differences between these measurements of gain agree with several previous investigations, but individual variation around the average difference was smaller than previously reported.