Active reduction of low-frequency tire impact noise using digital feedback control

Feedback control theory is used to develop an active noise control system to reduce transient-induced road noise in a vehicle interior. The system consists of a detector microphone, a high-speed digital controller, amplifiers, an analog smoothing filter, and a headphone. The digital control algorithm uses the output of the microphone combined with the past history of the control signal to calculate the current value of the control signal. This signal is passed through a low-pass filter (to smooth the steps resulting from the digital-to-analog conversion) and then amplified and sent to the headphone near the driver's ear. Two control algorithms are evaluated. A proportional-integral controller reduces the noise by about 5 dB over the 20-to-60 Hz range. A modified generalized minimum-variance controller is able to reduce the noise by about 10 dB for the 25-to-60 Hz range.<
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