ACTIVE CONTROL OF ROAD NOISE INSIDE VEHICLES

An active sound control system has been developed for automobiles whic h uses interior loudspeakers to counteract the low-frequency rumble of road noise when driving on typical road surfaces. Reductions of aroun d 7 dB of A-weighted sound pressure level in the range 100-200 Hz were measured using the system. Six accelerometers were attached to the ve hicle structure to detect road-induced vibration and to provide refere nce signals for a feedforward control strategy. In this paper the desi gn basis of the control system is set out and the theoretical and prac tical limitations inherent in this approach are examined. It is seen t hat key issues are (1) the placement of reference accelerometers for m aximum multiple coherence with respect to the interior noise to be att enuated, and (2) adequate time advance of the reference signals to all ow the controller to act in real time.