Enhancing microperforated panel absorption by subdividing the backing airspace into channels and resonators

Microperforated panel absorbers are easily tuned by varying the depth of the airspace behind the panel. In addition, it has been shown that subdividing the airspace behind the panel into a number of smaller cavities improves the microperforated panel absorber performance by preventing grazing wave propagation in the vicinity of the panel. In this work, different strategies for subdividing the airspace and varying the cavity depth behind the microperforated panel are considered. These include multi-depth channels, Helmholtz resonators, tapered or conical channels, and double leaf configurations. In each case, the absorbers are modeled using plane wave strategies, and normal incident sound absorption is measured in an impedance tube. Following this, the absorbers were implemented inside of a small enclosure and the insertion loss for the different treatments are compared. Sound absorbers are developed which greatly improve the broadband frequency attenuation compared to the unpartitioned case.