A Review of Current Techniques for Measuring Muffler Transmission Loss

TLDR: In this paper, two alternative measurement approaches are considered, which do not require an anechoic termination: the two load method and the two source method, which can be used to measure both transmission loss and the four-pole parameters of a muffler.

Abstract: The most common approach for measuring the transmission loss of a muffler is to determine the incident power by decomposition theory and the transmitted power by the plane wave approximation assuming an anechoic termination. Unfortunately, it is difficult to construct a fully anechoic termination. Thus, two alternative measurement approaches are considered, which do not require an anechoic termination: the two load method and the two-source method. Both methods are demonstrated on two muffler types: (1) a simple expansion chamber and (2) a double expansion chamber with an internal connecting tube. For both cases, the measured transmission losses were compared to those obtained from the boundary element method. The measured transmission losses compared well for both cases demonstrating that transmission losses can be determined reliably without an anechoic termination. It should be noted that the two-load method is the easier to employ for measuring transmission loss. However, the two-source method can be used to measure both transmission loss and the four-pole parameters of a muffler.