Equivalent Circuit Method Based Double Layer Micro-perforated Panel (MPP) Design to Widen the Sound Absorption Bandwidth

Acoustical solutions that occupy minimum space and simultaneously allow for flexibility in interior spaces are not feasible by using thick absorbers like conventional porous and fibrous materials. Micro-perforated panels are an excellent alternative to those classical materials due to their environmental friendliness, design flexibility on various materials, and easy installation. However, they come with the handicap of having a very narrow absorption frequency bandwidth. This study explores two inhomogeneous microperforated layers arranged in a cascade with different back cavities in order to widen the sound absorption bandwidth. This serial-parallel architected MPP system is investigated by mathematical models using Maa's model for a single MPP and the Equivalent Circuit Method (ECM). The numerical results were validated through experiments for normal sound incidence in the impedance tube using the transfer function method. Increasing the back cavity length of the MPP having a higher perforation ratio and larger holes results in a higher absorption in the high-frequency range. In contrast, combinations of larger cavity lengths and smaller perforation ratios are more effective in the low-frequency spectrum. By tuning the design parameters of those structures, it is possible to achieve wideband absorption by fibreless materials for room acoustic applications.