Concerns over the health risks, flammability, and limited low-frequency efficiency of fiber absorbers have encouraged the use of micro-perforated panels (MPPs). However, their performance is often limited by narrow absorption bandwidths. This study developed a heterogeneous parallel MPP absorber and evaluated its acoustic performance using impedance tube measurements, finite element method (FEM), and equivalent circuit method (ECM) models. Response surface methodology (RSM) was employed to optimize design parameters. Optimization results revealed a strong correlation between resonance frequency and perforation ratio. A configuration with perforation ratios of P1 = 2% and P2 = 0.6% provided the most favorable half-absorption bandwidth (α ≥ 0.5). Increasing hole diameter at lower perforation ratios broadened the absorption region and enhanced peak intensities; at 430 Hz, an enlarged d2 led to both higher absorption and wider bandwidth. Larger depth differences between the two MPP layers further expanded the absorption range. The final fabricated design incorporated hole diameters of 0.35 mm and 0.7 mm, perforation ratios of 1.8% and 0.8%, and cavity depths of 20 mm and 40 mm. This configuration achieved an average sound absorption coefficient of 0.618. Impedance tube tests showed absorption peaks of 0.96, 0.84, and 0.95 at 596 Hz, 1184 Hz, and 1440 Hz, respectively. Half-bandwidth absorption (α ≥ 0.5) was consistently observed across 400–1600 Hz, with experimental, FEM, and ECM results in close agreement. In conclusion, this MPP offer a safer and more robust alternative to fiber absorbers, the proposed heterogeneous parallel design expanded the half-absorption bandwidth up to threefold, significantly enhancing low-frequency and broadband performance.
Hashemi et al. (Sat,) studied this question.