Effects of wall admittance changes on duct transmission and radiation of sound

This paper is concerned with the effect of changes in duct wall acoustic properties on the transmission of sound through ducts. Two special problems are considered. The first problem is that of a rectangular infinite-length duct with airflow and a single change in duct wall acoustic admittance. The second problem is that of an axisymmetric field in a finite circular duct without airflow and with an arbitrary number of duct wall acoustic admittance changes. Results for the first problem show the effect of wall admittance change and flow on the acoustic power transmission within the duct. Results for the second problem show the interactive effects of multiple duct liner sections on power radiated from a finite duct.