Sound and Vibration Transmission through a Rectangular Double Wall by Statistical Methods: Theory and Experiment

Abstract

The existence of a great many modes in a randomly excited complex system makes a detailed classical modal analysis almost intractable. However, the existence of groups of similarly excited modes allows certain averages of the response to be found, as for response of a cylindrical shell to jet noise [A. Powell, in Random Vibration, S. H, Crandall, Ed. (Technology Press, Cambridge, Mass.), Chap. 8], and for the excitation of a structure by a reverberant acoustic field [R. H. Lyon and G. Maidanik, J. Acoust. Soc. Am. 34, 623–639 (1962)]. For sound transmission through a rectangular double wall, this technique gives results that agree within experimental error of measured transmission loss: much better than conventional loss estimates. Experiments have confirmed that the product of modal “density” and average joint acceptance of the first panel is the most important quantity in determining the transmission characteristics of the wall. [Partial support by the U. S. Office of Naval Research.]