This paper details how transmission and insertion loss can be defined for the multi-inlet case. Two different procedures are used for calculations and are compared against one another. The first is an impedance matrix approach that has been proposed in the past and is especially suitable for deterministic approaches like BEM. The other is a superposition method that does not require assembling or inverting a matrix. Though each approach can be extended to the n-inlet situation, the superposition approach is mathematically simpler but requires the source impedance to be known a priori. Transmission and insertion loss can be determined using either method, and results using either method are shown to be equivalent. The methods are demonstrated and compared for a two-inlet one-outlet expansion chamber.