Hua, X., Herrin, D., and Jackson, P., "Enhancing the Performance of Microperforated Panel Absorbers by Designing Custom Backings," SAE Int. J. Passeng. Cars - Mech. Syst. 6(2):1269-1275, 2013, doi:10.4271/2013-01-1937.
Micro-perforated (MPP) panels are acoustic absorbers that are non-combustible, acoustically tunable, lightweight, and environmentally friendly. In most cases, they are spaced from a wall, and that spacing determines the frequency range where the absorber performs well. The absorption is maximized when the particle velocity in the perforations is high. Accordingly, the absorber performs best when positioned approximately a quarter acoustic wavelength from the wall, and larger cavity depths improve the low frequency absorption. At multiples of one half acoustic wavelength, the absorption is minimal. Additionally, the absorption is minimal at low frequencies due to the limited cavity depth behind the MPP. By partitioning the backing cavity, the cavity depth can be strategically increased and varied. This will improve the absorption at low frequencies and can provide absorption over a wide frequency range. In this work, backing substrates have been developed to enhance the absorption performance. Maa's model is first reviewed. Then, different MPP and backing substrate combinations are analyzed using Maa's theory and the boundary element method. The broadband absorptive behavior is validated via measurement in a square impedance tube. Measured results agree reasonably well with analysis.