Effect of vibration of porous absorbent layers in the cavity of a multiple‐leaf structure on its acoustic properties

Porous absorbent layers are often used in the cavity of multiple‐leaf acoustic panels in buildings to reduce the sound power radiated by the panels or to enhance the panel absorption. It is known that bulk vibration of the porous layer can result in the reduced transmission loss of the multiple‐leaf acoustic panel. This work presents a simple method to account for the effect of the bulk vibration of the layer on its acoustic resistance. In this method the ‘‘modified’’ flow resistance of the layer is defined as the real part of the parallel impedance in the electro‐acoustical equivalent model. The model relates the impedance to the flow resistivity and the density of the porous layer. The ‘‘modified’’ flow resistance is then used to predict the propagation constant and the characteristic impedance of the material using the appropriate model for sound propagation in rigid‐frame porous materials. As an application, the effect of a porous layer in the cavity of double‐leaf panels on the radiated sound power i...