Acoustic Reciprocity of Large Three-Port Silencers

It is quite common for large mufflers or disk silencers used in power generation to have two large inlets or two large outlets. The large inlet/outlet diameters may result in a plane-wave cut-off frequency as low as a few hundred Hz, while the frequency range of interest may go above 8000 Hz. Higher-order modes must be considered in the transmission loss (TL) computation. In this paper, we study the acoustic reciprocity of large three-port silencers using the reciprocal identity. It is found that TL may or may not remain the same when the inlets and outlets exchange sides. The TL reciprocity depends on whether there is a reflective symmetry plane and whether the frequency exceeds the plane-wave cut-off frequency or not. The theoretical study is validated by the boundary element method (BEM) using the impedance-to-scattering matrix method and the finite-element method (FEM) using the perfectly matched layer boundary condition.