An extensive theoretical and experimental investigation has been carried out into the mechanisms of transmission of internally propagated sound through the walls of air-conditioning ducts with rectangular, circular, and flat-oval cross section. The insertion loss of external acoustic lagging on the three types of duct has also been studied. In all cases, prediction methods have been devised and compared to experimental data. Generally good agreement has been noted. In this paper, the major results of the project. are summarized.

Units: Dual