SPATIAL AND TEMPORAL FILTERING FOR FEEDBACK CONTROL OF ROAD NOISE IN CARS

Active noise control systems offer a potential method of reducing the weight of passive acoustic treatment and, therefore, increasing vehicles’ fuel efficiency. The widespread commercialisation of active noise control has, however, not been achieved partly due to the cost of implementation. To achieve cost-effective control of road noise, a feedback control strategy is presented which employs the array of microphones and the car audio loudspeakers common to a feedforward engine noise control system. The proposed system weights the contributions from the error microphones and the loudspeakers to increase the magnitude of the open-loop response over the bandwidth where noise attenuation is required, as in modal feedback control. This spatial filtering technique is combined with temporal filtering to further enhance the magnitude of the open-loop response over the targeted bandwidth and to compensate for the phase response of the control loudspeakers. The proposed feedback control system is shown to achieve reductions of up to 10 dB in the composite error signal, but only reduces the sum of the squared pressures by around 3 dB over a very narrow bandwidth.