Sound transmission through elastic solids and porous media having an elastic frame involves longitudinal and transverse waves. A modelling of sound propagation through layers of these media by transfer matrices, which is equivalent to a representation by analogous multi-port circuits was performed previously. The different ports of the circuits are related to the normal and the tangential strains and velocities on the two faces of the layers. The use of impedance matrices instead of transfer matrices shows that the coupling between the normal and the tangential conjugate variables is antireciprocal, and is reciprocal for conjugate variables having the same nature. Moreover, it can be proven that the transmission loss through stratified materials in contact with the same fluid on the front and the rear face is the same in opposite directions of propagation.