Diffuse Field Sound Absorption of Microperforated Panels with Special Backings

Microperforated panel absorbers are best considered as the combination of the perforate and the backing cavity. They are sometimes likened to Helmholtz resonators. This analogy is true in the sense that they are most effective at the resonant frequencies of the panel-cavity combination when the particle velocity is high in the perforations. However, unlike traditional Helmholtz resonators, microperforated absorbers are broader band and the attenuation mechanism is dissipative rather than reactive. It is well known that the cavity depth governs the frequency bands of high absorption. The work presented here focuses on the development, modeling and testing of novel configurations of backing constructions and materials. These configurations are aimed at both dialing in the absorption properties at specific frequencies of interest and creating broadband sound absorbers. In this work, several backing cavity strategies are considered and evaluated. Each configuration was modeled using plane wave simulation. The numerical results were then compared to experimental results at first at the single cell level using an impedance tube test, and sequentially a multiplicity of cells were tested in a reverberation room. Good correlation was found between the models and the experiments in terms of sound absorption coefficient. Using this approach, the sound absorption coefficient can be shaped over the frequency range while minimizing the space occupied.