Sound Propagation in Rectangular Parallel Layers Regarding the Effect of Boundaries

Recursion formulae are derived for the components of the sound propagation constants and distribution functions in rectangular arrangements with unequal parallel isotropic absorbent layers and flow channels. The absorbent layers are locally- or bulk reacting. Between the layers there may be “concentrated” impedances. The boundaries of the arrangements are piece by piece equally locally reacting impedances. Calculated normalized diagrams of the sound attenuation per unit of length are presented and discussed.