This paper proposes a noise insulation cavity composed of two parallel plates and a micro-perforated plate insertion parallel to the plates, which divides the cavity between the plates into two parts. A theoretical model was established that takes into account of all the couplings among the major parts of the structure, namely the two solid plates, the perforated plate, and the air cavity, together with the simply support boundary conditions. Numerical calculations were performed with different parameters of the micro-perforated plate including its position, perforation ratio, plate thickness, and hole diameters. The calculations indicated that the proposed double-panel structure with a micro-perforated plate insertion exhibited significant improvements in the sound transmission loss (STL) in certain frequency range as compared to a double- or triple-panel structure without a micro-perforated plate. Below 200 Hz the improvement in STL is mainly due to the weakening of the resonances by the energy dissipation of the perforated plate, while in the medium to high frequency range the STL enhancement is mostly due to the dissipation by the perforated plate in the broad frequency band. The theoretical results are in good agreement with the experimental results.
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