A duct 26 has circumferentially distributed features capable of scattering acoustic energy associated with fluid dynamic shocks 34 extending in a shock orientation direction D. Each feature is oriented, over at least a portion of its length, substantially perpendicular to the shock orientation direction. The features may be splices 42 used to connect segments of an acoustic liner 30, partitions 56 in a stability enhancing casing treatment 32, or other features capable of scattering acoustic energy associated with shocks.