Transmission loss calculation of a pipe with dissipative silencer containing porous materials

Various types of silencers have been used to reduce noise transmitted through pipe system. In particular, a dissipative silencer containing absorbing materials inside has an ability of noise control by transferring acoustic/vibrational energy to thermal energy. In this study, the acoustic performance of a dissipative silencer lined with two-layer absorbing materials is investigated. Herein, the absorbing materials in the form of a polymer foam are considered as a porous medium composed of a solid polymer skeleton and internal pores. From the boundary conditions at the rigid wall and the interfaces between the porous materials, eigenvalues and eigenfunctions in the dissipative silencer are determined. Finally the transmission loss is obtained through the mode matching method. The effects of geometry and acoustic properties of the porous medium are also discussed.