A Simple Method for Measuring Muffler Transmission Loss With PU Probes

The conventional approaches for measuring muffler transmission loss based on measurement in impedance tube are mainly decomposition methods and transfer matrix method. The decomposition method needs an anechoic termination, but it is not easy in some cases particularly for low frequency measurement. Two-load method and two-source method based on transfer matrix techniques are considered to be an alternative approach which does not require an anechoic termination. PU probe can measure both sound pressure and particle velocity, which is applied to some acoustic measurement such as absorption coefficient in recent years. A straightforward method for measuring muffler transmission loss by two PU probes measuring particle velocity at the inlet and outlet of muffler is presented. The four-pole parameters of the muffler can be calculated directly. The transmission loss measured by the PU method agrees well with the result measured by conventional four-pole method and FEM result. To instruct the approach, the influence of measurement distance between PU probe and the inlet or outlet of muffler and ambient noise are analyzed, which gives comprehensive suggestions for measurement set up.