Enhancing low-frequency sound absorption of micro-perforated panel absorbers by combining parallel mechanical impedance

Micro-perforated panel (MPP) absorbers apply to sound absorption performance at the medium and high frequency, but is not ideal for low-frequency sound absorption performance. Meanwhile, multiple pieces of mechanical impedance and a MPP in series occupy too much volume, which wastes cost and resource. Based on these, a parallel mechanical impedance structure is arranged in the cavity of the micro-perforated panel to form a composite structure, the mass of every mechanical impedance is 6.4 g. A preliminary study on composite structure and a corresponding calculation model is established. Then the acoustic impedance of the whole structure is calculated by using the transfer matrix method and finally the sound absorption coefficient is measured by using standing wave tube. Experiment results show that three sound absorption peaks appear at the low frequency from 200 Hz to 600 Hz. The first peak at 0.85 or more, and the second and the third peaks are between 0.4 and 0.6. The calculation model is in agreement with the experimental results, thus proves the feasibility of the composite structure to improve low-frequency sound absorption performance.