In recent decades, the number of light-weight building has increased. These walls are not well-suited sound insulation. For this reason, the multi-layer walls used in light-weight buildings. The multi-layer wall consists of panels and cavities, and porous materials are also used around the perimeter of cavities to absorb the sound energy. A large amount of sound transmission loss has increased by the cavity. Statistical energy analysis is a well-suited method for the prediction of sound transmission loss. This method has several limitations such as disability to use for complex geometry and does not consider the thickness of the cavities. SmEdA is an improved method derives from SEA. This method does not assume equipartition of modal energy, and it can be used to calculate complex cases. Another feature of SmEdA is mid-frequency analysis and its good accuracy in this interval. In this research, sound transmission loss has been calculated by SmEdA, SEA, Cremer, and mass law for single-layer and double-layer walls and compared with experimental data. Transmission loss of the triple-layer wall has only been estimated by SmEdA and SEA. SmEdA result of the double-layer wall has been verified by experimental data, SEA, Cremer, and Mass-law methods. As expected SmEdA has a more precise answer in low-frequencies and near the critical frequency of panels. SmEdA has slightly different answers in the double-layer wall, but results have significant different in triple-layer. Sound transmission loss has consistent with experimental and theoretical results. SmEdA computes time is considerably less than FEM, and much than SEA. The sound transmission loss of the double-layer wall and triple-layer wall has been calculated by SmEdA for the first time. Also, the effect of the thickness of the cavity has been investigated. If the thickness of the cavity widens more than a certain amount, the amount of sound transmission has little effect on the sound transmission loss in the walls. Keywords: Acoustic, Statistical Energy Analysis, Sound Insulation, Vibro-acoustics, Sound transmission loss
