Analysis of a perforated panel for the correction of low frequency resonances in domestic rooms

Perforated panels can be used as devices for the selective acoustic correction of rooms. Unlike panels made by porous materials, they work principally at low and middle frequency, and are acoustically inert at high frequency. For this reason, their main application is for the correction of modal resonances of rooms. Perforated panels consist of one layer of porous (dissipative) material and one of air, closed by a perforated plate and placed against a rigid wall. When this device is invested by a sound wave, the inside air resonates at a specific frequency, and a much energy is absorbed near this resonance frequency. Although perforated panels are used at both low and middle frequencies, there seem to be no studies in the literature about their modeling at low frequency, partly because it is very difficult to make experiments in this part of the audio spectrum. In particular, classical literature models, developed thinking to middle frequency behavior [

1

], [

2

], [

3

], do not perform well, in comparison with experimental and numerical results, when applied to study such low frequency devices. Here, we present an analytical and a numerical approach (this last based on the finite element method), developed in [

4

], for predicting the sound absorption of a perforated absorber system at low frequency. After validating the capabilities offered by the finite element technique, comparisons are made between the results of numerical analyses performed on both complete coupled acousticstructural and simplified models. A new, simple analytical algorithm for the design of these panels, based on the acoustic impedance method, is also presented. Finally, we briefly discuss the results of a method for the experimental measure of the acoustic impedance of perforated panels at low frequency, a method that has never been used to such a purpose, so far, to the best of our knowledge. Our numerical and analytical results are finally compared both with these experimental data and with the results of literature models [

1

], [

2

].