Reduction of sound radiated from vibrating structures via active control of local volume velocity

A new active noise-control technique has been developed for control of low-frequency sound generated by vibrating surfaces. The technique is based on minimizing the volume velocity. Noise reduction is achieved by distributing an array of control devices over the surface of the radiating structure (e.g. an aircraft fuselage interior). Each device consists of a motion-sensing mechanism, an analog control circuit, and a loudspeaker. The loudspeaker is driven such that it reduces the volume velocity of the radiating structure within its close proximity. This paper presents the theory behind this approach, as well as an experimental verification of this concept using a 10 in. uniformly vibrating circular plate and a single noise-control device. Broadband (50-500 Hz) sound reductions in the range of 10-20 dB were achieved over a wide spatial area. Since, in the final implementation of this concept, multiple devices will be employed on a nonuniformly vibrating structure, simulations of the performance of one, two, four, and six devices on a vibrating rectangular plate are presented.