Modeling parallel arranged transparent micro-perforated panels to enhance low-mid frequency sound absorption

Abstract

Passive absorbers such as fibrous or porous materials are indispensable for high-frequency damping noises; still, problems are increasingly found at low frequencies. Resonant structures, such as membranes, Helmholtz resonators, and micro-perforated panels (MPPs), are usually used for treating the latter issues. These reactive structures are mass-spring systems with damping to absorb the system's resonant frequency, offering only narrowband absorption. For the sake of broadening the absorption bandwidth, a series of structures based on MPP networks in series and parallel have been explored to introduce multiple resonances. The current study examines the computational modeling of four parallel arranged transparent MPPs with different hole sizes, perforations, and back cavities. A prototype of this absorber is machined by laser and CNC techniques and tested in an impedance tube. The experimental data obtained from using the transfer function are in good agreement with the absorption performance calculated by the electro-acoustic equivalent circuit model (ECM). Results show a wider half absorption bandwidth of the overall system for more than 3 octaves (from 160 Hz to 1120 Hz). The initial findings enhance the possibility of designing single-layer absorbers that are wideband, tunable, and free from porous/fibrous materials.