Acoustical modeling of flexible perforated screens attached directly to elastic porous materials

Perforated screens are frequently used to face sound absorbing porous materials since they serve both to protect the porous material and to enhance its effectiveness at low frequencies. Recently, exact theories describing the combination of a perforated screen and fibrous materials that can be modeled as equivalent fluids have been presented for both normal and arbitrary incidence angles. In this paper a similar analysis is presented that is appropriate when the sound absorbing material is an elastic porous material. The perforated screen itself is modeled as an Euler–Bernoulli panel whose stiffness and mass per unit area are modified by its degree of perforation. The boundary conditions describing the interaction of the elastic porous material and the screen require, among other things, that the velocities of both the solid and fluid phases of the porous material are simultaneously equal to the normal velocity of the nonperforated area of the panel. In addition, the volume velocity of the air within the ...