Effect of the Porous material modeling on the external sound field

Porous materials are widely used in noise control applications for reducing the reverberation acoustic field in closed space, the noise propagation inside dissipative mufflers or the panel vi-bration. One difficulty in noise control problems is the prediction of the real sound-absorbing capacity of porous materials before installing them. Usually, to reduce computational time, porous materials are simulated in numerical models (such as FEM, BEM, ray tracing) as an impedance plane or by choosing an absorption coefficient value. In previous studies, however, the authors investigated about the influence of sound source posi-tion and non-acoustic properties of a porous material on its surface acoustic impedance and its sound absorption coefficient. The main result is that, for a given frequency, its acoustic properties change and therefore is generally wrong to assume a single value for the surface acoustic imped-ance and/or the sound absorption coefficient to characterize the behaviour of the whole porous material. In this work, it will be reported some features about the errors in choosing a single value for the surface acoustic impedance instead of a suitable modelling of the porous material. The differences depend on the behaviour of the porous material (local or non-local reactive) and the height of the sound source from its surface.