Many techniques for controlling the noise radiated by large structures require a large number of inputs to the controller to produce global attenuation. Unfortunately, processing the large number of inputs required is often beyond the capabilities of current controllers. In attempting to overcome this problem, many researchers have adopted various modal-filtering-type techniques. Such techniques involve resolving a small number of important global quantities (traditionally structural modes) from a large number of sensor measurements. However, current approaches require detailed structural information at the design stage. Determining this for complex, real-world structures may be very difficult, preventing many techniques from going beyond the laboratory. The technique presented here outlines a new sensing system strategy, where the radiated sound field is decomposed using multipole radiation patterns, thereby alleviating the need for detailed structural information. Simulation and experimental results are presented.

This paper considers the design of a vibration absorber to reduce structural vibration at multiple frequencies, with an enlarged bandwidth control at these target frequencies. While the basic absorber is a passive device a control system has been added to facilitate tuning, effectively giving the combination of a passive and active device, which leads to far greater stability and robustness. Experimental results demonstrating the effectiveness of the absorber are also described.

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Scaling laboratory-sized active noise control systems into industrial-sized implementations is a difficult exercise. Problems relating to sensing system design account for some of the difficulty. In the first part of this paper, an alternative approach to sensing system design was presented where acoustic radiation patterns are decomposed using fundamental acoustic quantities, rather than structural modal based quantities. In this paper, the approach is tackled in the acoustic domain instead of structual vibration. The technique has been simulated in the time and frequency domains using acoustic sensors and implemented experimentally.

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