MIMO design of Active Noise Controllers for car interiors: Extending the silenced region at higher frequencies

Active Noise Control can provide damping of low-frequency noise in car compartments by feedforward or feedback control. The complicated sound field in reverberant environments limits the spatial volume of efficient sound control. At higher frequencies, damping is in general possible only within a small volume around a control microphone when using a single loudspeaker to produce the control signal. We here investigate how the spatial volume of control, as well as the upper limiting frequency, can be increased by using MIMO feedforward control that uses all loudspeakers of a premium car HiFi system. The results indicate that performance is improved for narrowband as well as broadband noise, resulting in a considerable noise reduction within a 0.3 × 0.3 m area. Compared to a corresponding SISO design that uses one loudspeaker and is optimized for one measurement position, the measured noise damping is improved and the upper limit frequency for control over the whole area is more than doubled, from 200 Hz to 450 Hz. The design requires high-precision identification of acoustic transfer functions from all involved loudspeakers as well as accurate modeling of noise paths.