Statistical energy analysis (SEA) is used to model sound transmission through double leaf lightweight partitions. It is found that the best SEA model depends on the frequency range considered and the method of construction. At low frequencies the wall can be modelled as a single subsystem while at higher frequencies it should be modelled as a number of interconnected subsystems. The structural connection between the two panels can be modelled either as a series of independent points or as a line connection, depending on the nail spacing. The results show that the basic SEA model is appropriate for this type of structure and that structural coupling can be accurately predicted. However, it was found that the theory for transmission into (and out of) large rooms cannot always be used with confidence to predict transmission into (and out of) a cavity. The error in this transmission path can lead to large errors when predicting transmission through the complete double wall if transmission is dominated by transmission paths involving the cavity.