ASA 126th Meeting Denver 1993 October 4-8

5aNS11. Active noise control applied to extended sources in a half-space.

Steve Shepard Kenneth A. Cunefare

The George W. Woodruff School of Mech. Eng., Georgia Inst. of Technol., Atlanta, GA 30332-0405

Recent work adapted free-field boundary element method-based optimal active noise control techniques for application in a half-space with a rigid or pressure release boundary. Here the required control source strengths and relative phases for active noise control applied to a rectangular solid above a rigid plane are investigated. It is assumed that one face of the solid is radiating harmonically with known surface normal velocity. The existence of unique behavior, as compared to free-field conditions, for the control source strengths and achievable power reduction due to the presence of the plane is demonstrated. This unique behavior occurs at and near certain discrete frequencies. These frequencies are not the characteristic frequencies of the Helmholtz integral for the rectangular solid; rather, they are related to the particular noise source velocity distribution and control source distribution. Finally, the half-space control formulation is employed to evaluate data from an experiment conducted in a hemi-anechoic chamber.