Enhancing micro-perforated panel attenuation by partitioning the adjoining cavity

The sound attenuation performance of micro-perforated panels (MPP) with adjoining air cavity is investigated for a plenum. The sound field inside of a plenum is compared for two cases. In the first case, the plenum is treated with an MPP and adjoining air cavity without any partitioning. For the second case, the adjoining air cavity is partitioned into a number of sub-cavities. The resulting sound pressure fields indicate that partitioning the adjoining air cavity increases the overall sound attenuation due to the MPP by approximately 4 dB. The explanation for this phenomenon was investigated by measuring the sound pressure level on planes in front of the MPP. Additionally, boundary element analyses were conducted to simulate the effect of the MPP and adjoining cavity with and without partitioning on the sound field in the plenum. It was demonstrated that a MPP can be modeled as a transfer impedance and that partitioning the adjoining cavity enhances attenuation to acoustic modes that propagate transverse to the MPP.