Sakamoto, K. and Inoue, T., "Development of Feedback-Based Active Road Noise Control Technology for Noise in Multiple Narrow-Frequency Bands and Integration with Booming Noise Active Noise Control System," SAE Int. J. Passeng. Cars - Mech. Syst. 8(1):1-7, 2015, https://doi.org/10.4271/2015-01-0660.
When a vehicle is in motion, noise is generated in the cabin that is composed of noise in multiple narrow-frequency bands and caused by input from the road surface. This type of noise is termed low-frequency-band road noise, and its reduction is sought in order to increase occupant comfort. The research discussed in this paper used feedback control technology as the basis for the development of an active noise control technology able to simultaneously reduce noise in multiple narrow-frequency bands. Methods of connecting multiple single-frequency adaptive notch filters, a type of adaptive filter, were investigated. Based on the results, a method of connecting multiple filters that would mitigate mutual interference caused by different controller transmission characteristics was proposed. This method made it possible to implement controllers with amplitude and phase characteristics in multiple narrow-frequency bands corresponding to design values, and to achieve the target noise-reduction. Additionally, in feedback-based road noise control, the amplitude of the control output signal changes drastically depending on the frequency characteristics of the road surface. When this technology was integrated with the already-commercialized booming noise control system, a method to adjust the range of each controller output automatically was applied, achieving integration while balancing noise reduction performance under normal conditions with control stability when the vehicle passes over a large-input surface.