A spinning mode synthesizer has been developed to study the propagation of complex higher order modes in cylindrical ducts. This device has been shown (“The Design, Development, and Use of a Spinning Mode Synthesizer,” M. J. Oslac, and J. M. Seiner, Proc. Purdue Noise Conf.) to be very useful in studying the behavior of spinning waves which are believed to be the principle component of the noise generated by fans, compressors, and jet engines. In this investigation, the spinning mode synthesizer was coupled to a 12-in.-diam cylindrical duct 8 ft long, which was in turn coupled to an 8-ft-long, 18-in.-diam cylindrical duct having an anechoic termination. Single higher-order modes were then propagated down the infinite duct having at its center an abrupt cross-sectional change. Radial, axial, and circumferential measurements were made in both the 12 and 18-in. ducts. Transmission, reflection, and generation of modes at the discontinuity are compared with a mathematical model. [This research is being conducted under a NASA grant.]