Sound absorption characteristics of a honeycomb-backed microperforated panel absorber: Revised theory and experimental validation

A microperforated panel (MPP) absorber is known as one of the most promising alternatives of the next-generation sound absorbers. However, MPPs are usually made of thin limp materials and need to be reinforced by a supporting element. The authors proposed to use a honeycomb attached behind an MPP for this purpose, and have shown that the honeycomb in the back cavity of an MPP absorber is not only useful to stiffen the MPP but improves its sound absorption performance, particularly at low frequencies. In the authors" previous studies an electro-acoustical circuit model was used to analyse its sound absorption characteristics, however, the model inevitably includes an approximation, and more exact theory needs to be established for better prediction of its characteristics. In this paper, the absorber is analysed with the wave theory based on Helmholtz-Kirchhoff integral equations. First, the formalism based on the Helmholtz-Kirchhoff integral is presented. Next, an experiment is made to validate the theory. Finally, a parametric study is made to discuss the effect of the parameters of the sound absorbing system on its sound absorption characteristics.