Design charts for low frequency acoustic transmission through the walls of rectangular ducts

Abstract

“Design charts” are presented here, from which the low frequency acoustic transmission loss of the walls of rectangular ducts may be found. The upper frequency limit on the applicability of this method is at cut-on for the first cross mode in the equivalent rigid walled duct, and it is shown how a quasi-static theory can easily be used to extend the results, as obtained from the charts, to lower frequencies. The data are given in terms of non-dimensional parameters, in order to keep the number of charts to reasonable proportions. Two “design examples” are described here, and it is felt that the accuracy in the use of the charts ought to be sufficient for most practical purposes.