Abstract: Based on the modal interaction method, this study presents a structural-a^oustic coupled model of a rectangular enclosure consisting of two flexible panels on opposite sides of the enclosure. A simplified relationship between the panel parameters and the NVH responses of the coupled system is derived. Using this modal, parametric studies aiming at reducing the total weight of the structure and simultaneously improving the NVH performance are conducted for cases of single flexible panel-single excitation (SPSE), dual flexible panel-dual excitation (DPDE) and dual flexible panel-single excitation (DPSE). For the SPSE and DPDE cases, it is found that in the low frequency range the sound level inside the cavity is most sensitive to the panel thickness, then to the panel modulus, and nearly independent of the material density. It is therefore concluded that a panel with larger thickness but lighter material may be able to reduce the structural weight and low frequency sound level simultaneously. For the DPSE case, proper lightweight design can enhance the coupling effect between the motions of the two flexible panels in certain frequency range, especially around the lower order modes of the panels and the cavity. This leads to both reduced modal response levels and pressure within the acoustic cavity. For mid to high frequencies, increasing the thickness and density of the panels is beneficial for all three cases in terms of reducing the noise level inside the cavity.