Modal and multichannel feedback control of road noise in a car

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. The active control of engine noise can be implemented cost-effectively by using the car audio loudspeakers as control sources and an array of low-cost microphones as error sensors. Such systems have been practically demonstrated, but without also controlling road noise their subjective benefits may be somewhat limited. The active control of road noise using the car audio loudspeakers and a feedforward control strategy has also been practically demonstrated. However, these systems require a number of accelerometers to be mounted to the vehicle’s structure to obtain a coherent reference signal and, therefore, lead to a significant implementation cost. To achieve cost-effective control of road noise, two feedback control strategies are investigated which employ the array of microphones and the car audio loudspeakers common to a feedforward engine noise control system. The first 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 application of this control system is limited to applications where a specific acoustic mode requires control. Therefore, a second, multichannel feedback control system is also presented. This system may achieve broadband control of road noise at the expense of controller complexity.