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Volume 126, Issue 6, December 2009
- ACOUSTICAL MEASUREMENTS AND INSTRUMENTATION 
Measurement of characteristic impedance and wave number of porous material using pulse-tube and transfer-matrix methods126(2009); http://dx.doi.org/10.1121/1.3242354View Description Hide Description
The time domain implementation of the transfer-matrix method developed by Song and Bolton [J. Acoust. Soc. Am.107, 1131–1154 (2000)] for measuring the characteristic impedance and wave number of porous materials is described in this paper. The so called Butterworth impulse is generated in a standing wave tube with a flat frequency response over a wide frequency range. With only two microphonemeasurements, the transfer matrix of porous layers can easily be determined through the calculation of complex amplitudes of incident, reflected, and transmitted pulses. The procedure has been used to measure the acoustical properties of a fiber material, and good agreement was found between measuredacoustical properties and predicted results by Delany and Bazley [Appl. Acoust.3, 105–116 (1971)] semiempirical formulas. Although the error associated with the sample-edge constraint still remains, the new method has a better frequency response as a result of the system calibration process, and the optimal inter-microphone distance is no longer required compared to the frequency domain implementation.