The propagation of sound in a circular duct of continuously varying cross-sectional area

Abstract A method has been developed for predicting the behaviour of sound propagating in a circular duct of continuously varying cross-sectional area. The method can accommodate higher order modes of sound and any arbitrary rate of flare can be examined. Essentially an approximation is made to the duct shape by a series of subsections whose sides are parallel to the axis of the duct. Small discontinuities occur at the end of each subsection. The equations governing the propagation of sound past each discontinuity and along each subsection are then solved. The usefulness and accuracy of the method were demonstrated by predicting the sound field produced by an exponential horn radiating into a free field. Several radial modes of sound were propagating in this case.