Wideband measurement of the acoustic impedance of tubular objects

Maarten van Walstijn, Murray Campbell, Jonathan A Kemp, David Sharp

Research output: Contribution to journalArticlepeer-review

22 Citations (Scopus)


A method is discussed for measuring the acoustic impedance of tubular objects that gives accurate results for a wide range of frequencies. The apparatus that is employed is similar to that used in many previously developed methods; it consists of a cylindrical measurement duct fitted with several microphones, of which two are active in each measurement session, and a driver at one of its ends. The object under study is fitted at the other end. The impedance of the object is determined from the microphone signals obtained during excitation of the air inside the duct by the driver, and from three coefficients that are pre-determined using four calibration measurements with closed cylindrical tubes. The calibration procedure is based on the simple mathematical relationships between the impedances of the calibration tubes, and does not require knowledge of the propagation constant. Measurements with a cylindrical tube yield an estimate of the attenuation constant for plane waves, which is found to differ from the theoretical prediction by less than 1.4% in the frequency range 1 kHz–20 kHz. Impedance measurements of objects with abrupt changes in diameter are found to be in good agreement with multimodal theory.
Original languageEnglish
Pages (from-to)590-604
Number of pages15
JournalActa Acustica united with Acustica
Issue number3
Publication statusPublished - 1 May 2005


  • acoustic impedance measurement two microphones four calibrations


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