Phase I of this study had examined the design characteristics of machinery enclosures as an application for noise control by active cancellation. Reduction of noise transmitted through structures is a need that pervades a wide variety of situations. In this approach, noise reduction at low frequency is achieved via active control concepts, and at high frequency--using passive control. Performance estimates for control demonstrate the need for multiple actuators to cancel enclosure transmitted noise throughout the active control frequency range over the full spectrum of spatial angles. In Phase II of this research project, the emphasis is on developing analytical and numerical models of three-dimensional enclosures and assessing the role of structural-parameters in achieving the objectives of a low- frequency noise filter; evaluating surface observer options; developing cost-effective approaches for actuating the surface panels; evaluating alternative sensors and design concepts for embedding them into a surface panel module; developing a specific design for a prototype enclosure including primary structure and surface modules with sensors and actuators; and experimentally evaluating the above concepts using the prototype enclosure.***//
