The experiment presented in this paper was to investigate and analyse the noise reduction at low frequency of porous material used to line the cavity between two panels of a double-panel structure. The effects of panel construction, fibreglass and cavity depth have also been studied. The structural-acoustic coupled system of a sandwich structure, backed by a rectangular acoustic cavity of rigid walls is discussed. It is found that the sound insulation of a combination of a stiff thick and a thin flexible plate panel, with air cavities and porous material in-between, is more effective than that of the conventional double-wall panel at low frequency.
