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The University of Southampton

Research project: Active Control of Road Noise in a Car

Currently Active: 

The use of active noise control in cars may allow manufacturers to remove traditional passive acoustic treatments and thus reduce weight and improve fuel efficiency.

Active noise control systems offer a potential method of reducing the weight of traditional passive acoustic treatments used in vehicles and, therefore, may improve 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 in the car cabin can be achieved by using the car audio loudspeakers to cancel out the pressures produced by the tonal engine orders at microphones positioned at the car headrests, as shown in the adjacent photo. This active control system can be implemented using a feedforward control algorithm in which a reference signal is provided from the engine tachometer. This system is relatively inexpensive to implement.

The active control or road noise is a more complicated task due to the unpredictability of road noise. In order to obtain a good reference signal for a feedforward controller it is necessary to mount a number of accelerometers to the vehicle structure and this is a relatively expensive requirement. This research project has investigated a number of different methods of implementing a low-cost active road noise control system including a modal feedback control system and local active noise control. However, the most promising method which achieves a good level of compromise between cost and performance is a multi-input, multi-output control system. This system attempts to cancel that noise at the headrest microphones and uses a further four low-cost microphones positioned close to the floor of the car cabin to provide time advanced information. The system thus requires very similar hardware to the engine noise control system and can be implemented at a relatively low-cost. The novel road noise control system is able to achieve an average attenuation in the road noise of around 3 dB.

Rear Headrest error microphones for active noise control system
Rear Headrest error microphones

Associated research themes

Acoustics, Mechatronics, Signal Processing and Control

Related research groups

Signal Processing, Audio and Hearing Group

Key Publications

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