Active control of the acoustic environment in an automobile cabin

摘要

The acoustic environment in an automobile cabin has a significant effect on the perceived quality of the vehicle. There are two components of the acoustic environment in the automobile cabin: the noise due to automotive processes and the sound produced by the car audio system. In both cases active methods can be employed to improve the acoustic environment and this thesis presents an investigation of both active control of automotive noise and active sound reproduction systems in cars. In the context of active noise control, cost-effective systems are investigated for the control of both engine noise and road noise. A model of structural-acoustic coupling is first derived and the effects of coupling on the performance of feedforward and feedback controllers is investigated. Feedforward control has been highlighted as a cost-effective method of controlling engine noise. In order to achieve low-cost active control of road noise, however, a number of multi-source, multi-sensor feedback active noise control systems are investigated. A modal feedback control system is investigated and shown to offer significant levels of control of a single dominant resonance. In general, however, a fully multi-input multi-output (MIMO) feedback controller is necessary to achieve control of the multiple resonances present in a road noise disturbance. Measurements have been conducted in a small city car to validate the proposed MIMO feedback controller and a real-time feedforward engine order control system has been implemented. Active control of sound reproduction has also been investigated with the aim of producing independent listening zones in the front and rear seats of the automobile cabin. Simulations have first been used to investigate the effect of implementing a personal audio system in a car cabin and to compare the performance of acoustic contrast and least squares optimisation strategies. In order to achieve control of the sound field over the full audio bandwidth two arrays are implemented, one employing the four standard car audio loudspeakers and one employing phase-shift loudspeakers mounted to the headrests. The performance of the system is validated using a real-time implementation in a people carrier.