W. T. Chu
Acoust. Lab., Inst. for Res. in Construction, Natl. Res. Council Canada, Ottawa, ON K1A 0R6, Canada
Using computer simulations, Bolton has shown that measurements with three equally spaced microphones may be used simultaneously to determine the complex propagation constant and the forward- and backward-going wave components in an impedance tube [J. S. Bolton and M. Kompella, J. Acoust. Soc. Am. Suppl. 1 84, S96 (1988)]. The impedance of the test material may then be determined. The practicality of this proposal has been studied in more detail, using both computer simulations (with realistic inputs containing random errors) and actual experimental implementation with the single microphone technique [W. T. Chu, J. Acoust. Soc. Am. 83, 2255--2260 (1988)]. Results indicate that the method is feasible provided that the microphone positions are properly chosen. This requirement will limit its application.