Abstract
In relation to reduction and passive control of noises emitted from ducts or openings of machineries, the acoustic field radiated from a flanged cylindrical duct having a coaxial cavity at the exit of the duct was investigated for various depths and radii of the cavity. Structures of the acoustic field generated by a sound source located at a distance from the exit were analyzed numerically using the finite difference method. Also, experiments were conducted to obtain the distribution of acoustic pressure levels and acoustic intensities around the exit using a three-dimensional intensity microphone system. It is shown that the cavity attached to the duct affects the acoustic field markedly and an appropriate configuration of the cavity reduces sound pressure level significantly. It is also shown that the acoustic field is well simulated by the present numerical calculation method.
