Insertion gain measured with three probe tube systems.

The study consisted of two experiments on the insertion gain measured with probe tube microphones. In experiment I, the insertion gain of the same mild gain hearing aid was measured twice on 12 subjects using three commercially available probe tube systems. Test-retest measurements were made by two different examiners. Mean test-retest differences were all less than 4 dB with 95% critical differences for these measures varying from approximately 3 to 8 dB depending upon the test system used. In experiment II, the three sets of probe tube measures of insertion gain were compared to behaviorally measured functional gain in 7 hearing-impaired subjects at several frequencies. There were no significant differences among the probe tube measures of insertion gain or between these measures and functional gain. Functional gain was significantly correlated with probe tube insertion gain for each device at frequencies from 500 through 4000 Hz.