Transmission loss defined as the ratio of incident power to transmitted power is obtained for the simple expansion chamber with multiple inlet and outlet ports. Transmission matrices corresponding to acoustic exhaust systems with multiple inlet and outlet ports are developed in the form of the rectangular matrices according to the number of inlet, outlet ports. For the cases that the number of inlet ports is not equal to that of outlet ports, transmission matrices depend on the input relations as well as the acoustic system parameters(i.e. geometry of the chamber, wall admittance, etc.), which makes the problem complicated. To illustrate the possible use of these transmission matrices, transmission losses of the simple expansion chambers with arbitrarily located inlet/outlet ports are examined. The simulation and experiment including the effects of higher order modes for the case that the number of inlet, outlet ports is less than or equal to two, have been performed to investigate the role of multiple inlet and outlet ports on transmission loss. One of findings associated with the characteristics of transmission loss of multiple inlets and outlets is that phase difference between inlet ports can significantly increase the transmission loss in low frequency range. Moreover, the locations of maxima and minima of the transmission loss for multiple inlet expansion chamber does not differ with those of expansion chamber with assumed equivalent inlet ports ; no phase difference.
