GLOBAL OPTIMUM ACTIVE NOISE-CONTROL - SURFACE AND FAR-FIELD EFFECTS

This paper examines the physical characteristics of global optimum active noise control on the surface and in the far field of extended radiators. Global optimum active noise control expresses the total acoustic power radiated by a collection of noise sources and active noise control sources with a quadratic equation in terms of source strengths or, for extended structures and control sources, surface velocities. Quadratic optimization theory is then used to obtain the secondary source strengths or surface velocities that yield the minimum total radiated power. The nature of the quadratic expression guarantees that the solution yields the global minimum, not simply a local minimum. The physical mechanism for optimum active noise control is the increased complexity of the combined sources. That is, with a suitable number of sources, a structure radiating like a monopole to the far field will radiate as a dipole after activation of the active noise control sources. While global optimum control is guaranteed to reduce the net power radiated by the control source/noise source combination, there is no guarantee that the intensity in all directions will also be reduced.