Reliability of Measures Obtained with the Zwislocki Acoustic Bride

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Abstract
An acoustic‐impedance bridge designed by Zwislocki recently became available. The bridge allows the specification of the absolute acoustic impedance of the human car by yielding independent measures of acoustic reactance and resistance. This measurement of absolute impedance requires an accurate measure of the volume of the external ear. The test‐retest reliability of volume measures, as well as those of resistance and reactance, was examined. Three examiners obtained volume measures by using two different techniques as well as measures of resistance and compliance (reactance) on 10 subjects in test and retest sessions. Results suggest that measurement of the volume of the ear canal is sufficiently repeatable to allow this procedure to serve as a first step in the measurement of absolute impedance with the Zwislocki bridge. Test‐retest reliability of the compliance measures was also high. Test‐retest measures of resistance yielded low correlations in spite of high interexaminer correlation in both sessions. It is postulated that unknown factors caused a real but nonsystematic shift in acoustic resistance over subjects, thus destroying test‐retest correlation while preserving high interexaminer correlation. Further investigation is required to establish the validity of this hypothesis, but it can be concluded that the bridge itself is a reliable measuring device.

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