Method to measure acoustic impedance and reflection coefficient

Douglas H. Keefe, Robert Ling, Jay C. Bulen

Research output: Contribution to journalArticlepeer-review

167 Scopus citations


A frequency-domain based system for measuring acoustic impedance and reflection coefficient is described. The calibration procedure uses a least-mean-squares approximation to the Thevenin parameters describing the source and receiver characteristics in which the data measured on closed, cylindrical tubes are matched to a viscothermal tube model. The system is intended for use in acoustical measurement in human ear canals, in which the cross-sectional area of the ear canal at the point of insertion is imprecisely known. This area is acoustically estimated from the impedance data, and the reflection coefficient is calculated in terms of this area and the impedance data. Measurements on a variety of closed tubes show the method is accurate over the frequency range investigated (< 10.7 kHz). The time-domain reflection function is evaluated by transforming the reflection coefficient from the frequency domain, but the finite bandwidth of the measured data limits the accuracy of time-domain response measurements. The method is well suited for frequency-domain measurements in human ear canals.

Original languageEnglish (US)
Pages (from-to)470-485
Number of pages16
JournalJournal of the Acoustical Society of America
Issue number1
StatePublished - Jan 1992
Externally publishedYes

ASJC Scopus subject areas

  • Arts and Humanities (miscellaneous)
  • Acoustics and Ultrasonics


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