Performance of multiple micro-perforated panels in a duct

Generalized formulation is developed analytically to calculate the transmission loss performance of a silencer by using multiple micro-perforate panel (MPP) array silencers in ventilation duct system. The device, based on single MPP design, consists of different expansion chambers with the side-branch cavities covered by micro-perforate panels of different properties. The theoretical model can also be simplified to evaluate the performance for normal plate silencer. With a preliminary result of two normal plates, it shows that the plate silencer can offer a wide stop band of 3.5 from low to medium frequency range when the length ratio is 1 to 4. Compared with same total length of a single plate, the stop band is improved by 25%. For the MPP silencer under similar condition, the stop band is also increased by 16%. Apart from the considerate increment of stop band, the bending stiffness requirement is also released by 35% and 40% respectively.