This study focuses on the improvement in the understanding of airborne noise transmission phenomenon in buildings, at low frequencies, under conditions of different architectural configurations. The effects of low-frequency noise have been of a particular concern because many kinds of structures have been inefficient in attenuating low-frequency noise, compared to other frequency components. Likewise the Sound Reduction Index is normally measured under diffuse field conditions and these calculations show that, at low frequencies, this is not the case. An acousticstructural coupled room-plate-room model, which allows variations in room size and shape, and partition properties to be considered, has been formulated and solved. Results of a parametric study show the effect of several configurations for a flexible partition (different geometric size and position in the common wall) and connected rooms (size and absorbing walls) on the Sound Reduction Index by averaging over 1/3 octave bands. Finally, a general discussion, based on the findings of the results obtained, is presented.