LAUSR

This paper describes the diffraction of the lowest plane wave propagating out of the opening of a semi-infinite hard duct that is symmetrically placed inside an infinite soft duct. The whole system forms a pentafurcated waveguide whose solution is given by eigenfunction expansion. The same method has been used to validate the results of a trifurcated duct problem previously tackled by using the standard Wiener–Hopf technique. Some graphical results showing the influence of waveguide spacing on the reflection coefficient are presented. We compared our results with the related existing work. We observe that the accumulative value of reflection for current pentafurcated duct is 1375.1, which is the greatest among the related trifurcated and existing pentafurcated ducts. Hence the soft lining on outer plates gives better results to attenuate the unwanted noise. These problems have application in acoustics.