An alternative approach to window ANC

Outdoor noise can enter an office workspace through an open window. An active noise Control system Is described that can provide global reduction in the workspace of noise from outside the window. The system uses (1) a microphone array outside the window to detect the magnitude and direction of incoming sounds; (2) a sparse array of loudspeakers in and around the window to radiate sound into the office space to cancel the entering outside sound, and (3) a processing system to derive appropriate signals from the microphone array to drive the speaker array to achieve cancellation. The sparse array leaves the window mostly open and unobstructed. Array shading coefficients that match the radiation pattern of the array to that of the window aperture can be derived in advance. ANC processing on each outdoor noise source provides the signals to drive the cancellation array. A feedforward system built to this design concept should provide reasonable cancellation with minimal window obstruction and fewer optimization channels than a more conventional window cancellation system.