A theoretical model of sound transmission across metal ties in a cavity wall is presented in which power flows across independent point contacts between the two leaves of the wall. From a knowledge of the mobilities of the walls and the tie stiffness, the power flow across the ties can be determined. The expression for the power flow is then used as part of a statistical energy analysis model which enables the performance of the entire wall to be computed. Transmission across the air was modelled as an equivalent tie. The stiffness of standard ties was measured as was the performance of a number of different walls with those ties. The measured results agreed well with the theoretical model, except when there were no metal ties. © 1995 Academic Press. All rights reserved.