Acoustical modeling of micro-perforated panel at high sound pressure levels using equivalent fluid approach

An acoustic impedance model to characterize micro-perforated panels at high sound pressure levels is proposed. The model uses a rigid frame porous medium, where the micro-perforated panel is modeled with an effective density, function of the frequency following the approach of Johnson-Allard and the equivalent fluid parameters such as the tortuosity and the flow resistivity are expressed as function of the incident sound pressure which is considered as a main variable. Unlike existing models which are limited to micro-perforated panels coupled to air cavity, the present model predicts correctly the acoustic response of micro-perforated panel backed by porous media which can be air cavity, porous material or resistive screen. Micro-perforated panel backed by porous media involves a distortion of the flow caused by the perforations through the porous media, thus the micro-perforated panel is modeled in this case using an equivalent tortuosity where a correction term is proposed to account for the flow distortion effect and it depends on the dynamic tortuosity of the porous layer and the incident sound pressure. The proposed impedance model is compared numerically with other existing nonlinear impedance models for different configurations of the micro-perforated panel. The results show a good agreement among each other for sound pressure levels up to 150 dB. In addition, experimental measurements were performed on several micro-perforated panels backed by air cavities or porous material using the classical impedance tube. A good correlation between theoretical and experimental results is obtained. Some validation and benchmarking results are illustrated and discussed in this paper. It is shown that the high sound pressure levels decrease the tortuosity and increase the flow resistivity of the micro-perforated panel. Furthermore, the acoustic energy dissipation by the micro-perforated panel absorber with a large perforation diameter which is low in the linear regime can become important and interesting at high sound pressure level.