Approximate asymptotic solutions for acoustic transmission through the walls of rectangular ducts

Approximate expressions—valid at sufficiently high frequencies—are obtained for the acoustic transmission loss of the walls of rectangular ducts. Single mode propagation inside the duct, both in the fundamental mode and in higher order modes, is considered and a multimode model is also proposed. These theories lead to very simple formulae for the transmission loss, which prove to be in tolerably good agreement with measurements.