This example demonstrates the propagation of sound in a dissipative waveguide. A duct with a square cross-section is considered. The side walls are lined with a locally reacting sound absorbing material. Using this example, several interesting physical phenomena that occur in waveguides such as dispersion, cutoff frequencies of the various transverse modes, and attenuation of sound etc. are explained. Analytical solution is derived and compared with Coustyx solutions. Excellent agreement is observed.

This example makes extensive use of the scripting feature of Coustyx to model side wall impedance that varies with frequency, and in functions for computing the transverse eigenvalues for use in the analytical solution.