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Measurement of transmission loss of materials using a standing wave tube

In this paper a measurement procedure for evaluating the normal incidence transmission loss of noise control materials using a four-microphone standing wave tube and an FFT analyzer is described. The mathematical formulation is based on the transfer matrix representation, which has been widely used in the past both to analyze and to measure the acoustical properties of flow system elements. The method described here differs from some earlier approaches that use a similar experimental setup in that knowledge of the tube termination condition is not required to ensure the accuracy of the result. Although the sound power transmitted through a sample in the tube depends in general both on its properties and on the tube termination conditions, the transfer matrix elements, which are used to calculate the transmission loss, are properties only of the sample.