This chapter presents an application of active noise control techniques for passenger comfort in cars. At the analysis stage nonstationary vibrations of the front and rear wheels are generated by nonuniform road profiles and change of vehicle speed. These propagate through the tyre and the complicated suspension system and finally generate structure-borne noise, impulsive noise, and other low-frequency noise in the interior of the passenger vehicle. These noises produce acoustical resonance in the interior of the passenger car and such resonant noise is called "road booming noise". Cancellation of this noise is the topic of this chapter.

14.1 Introdution

There are several characteristics of road booming noise. Independent vibrations of the four wheels generate it, so it can hardly be reduced by ANC with just one or two reference sensors. Second, the properties of road booming noise change as vehicle speed or road profile varies. And the system from the wheel vibration to road booming noise is not linear because of the complexity of the suspension system, nonlinear interaction between the structural vibration and the interior acoustics etc. We want to compensate for road booming noise, which has a strong correlation with the vibration signals measured at the suspension system. Active noise control of road booming noise is rather difficult to achieve because of its nonstationary characteristics. We developed a multi-input multi-output constraint filtered- x