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

5aNS8. Active control of energy density in three-dimensional enclosures.

Scott D. Sommerfeldt

John Parkins

Appl. Res. Lab. and Graduate Program in Acoust., Penn State Univ., P.O. Box 30, State College, PA 16804

Attenuating the sound pressure at a microphone in an enclosure typically results in a relatively small region of control, often referred to as a zone of silence. In an effort to increase the region of control for practical applications, as many as 30--50 microphones have been used to achieve a broader region of control. An alternative control method for achieving global control of the field, based on sensing and minimizing the total energy density at discrete locations, has been developed. Previous work using this method in one-dimensional enclosures has indicated that significant improvement in overall attenuation is possible. This improvement can be attributed to the fact that sensing the energy density monitors all of the modes of the enclosure, and thereby avoids the spillover problem which often plagues control systems that minimize only pressure. The work reported here extends the energy density approach to three-dimensional, rectangular enclosures. Numerical results are presented to compare the global attenuation achieved by minimizing the energy density and acoustic pressure at single and multiple discrete locations. These results are also compared with the control that one would achieve by minimizing the total potential energy in the enclosure.