An investigation of a theoretical tool for predicting performance of an active noise control system.

Active noise control is a topic of increasing interest for car manufacturers. In the lower fre-quency range, active control could relax the need for sound insulating materials, leading to lighter vehicles with lower fuel consumption. Here, we investigate further the possibility of using multiple loudspeakers with the aim of enlarging the spatial zones where sufficient noise suppression is achieved. A model-based Linear Quadratic design of a linear multiple-output feedforward regulator is used to approximate known noise paths to multiple measurement po-sitions by the combined secondary paths from the control loudspeakers. The attainable perfor-mance depends on the number and positioning of the control loudspeakers. Tools are needed for predicting and understanding the structural constraints on the attainable performance of the active control system. A measure of reproducibility of the primary paths between a noise source and a control area by a set of control loudspeakers has been investigated here. It uses the concept of an effective rank of the control system. With a given constellation of loudspeak-ers, the contribution of each loudspeaker to the possible attenuation of a disturbance has been analysed and the relationship between the reproducibility of the primary path and the achieved attenuation explored. The insights gained may result in a tool to help car manufacturers placing loudspeakers with both sound reproduction and active noise control in mind. 1.