Acoustic impedance of microperforated plates with stepwise apertures

Microperforated plates (MPPs) are efficient sound absorbers typically made of thin panels, which restricts practical application in engineering. This paper investigates MPPs with stepwise apertures on thick panels to enhance acoustic performance and overcome the lack of appropriate strength. Thermoviscous acoustic simulations of the MPPs demonstrate that the acoustic pressure, local velocity, and the power dissipation change abruptly at the step edges, similar as the behaviors at the inlet and outlet ends of the uniform perforations. The step generates additional acoustic impedance, which has a strong relationship with cross section ratio. Empirical impedance correction models for sharp-edged circular holes located concentrically on square or circular end panel are derived based on numerical simulations. Experimental data validate that the proposed models offer accurate prediction for acoustic impedance of MPPs with stepwise apertures.