ASA 127th Meeting M.I.T. 1994 June 6-10

5aNS6. Active control using only a layer of simple sources.

John B. Fahnline

Gary H. Koopmann

Ctr. for Acoust. and Vibration, 157 Hammond Bldg., Penn State Univ., University Park, PA 16802

Previous research in the area of active noise control has shown that the sound radiation from a vibrating body can be completely controlled using layers of simple and dipole sources located on a surface that completely surrounds the vibrating body. If complete control of the sound radiation could be achieved with simple sources only, the implementation of the control strategy will be considerably simplified because simple sources can be approximated with conventional loudspeakers. It is shown that complete control can be achieved when the simple source layer is very near the boundary surface of the vibrating body (assuming that the fluid coupling between the vibrating body and the surrounding fluid is negligible). When the simple source layer is not near the surface of the vibrating body, the control strategy fails at the resonance frequencies of the volume of fluid between the surface of the vibrating body and the layer of simple sources. The effect of approximating the continuous source distribution by a discrete source distribution is examined, and it is shown that the discrete sources can control the sound radiation effectively as long as there are an adequate number of sources distributed over the surface of the vibrating body.