# Laboratory Test of a Vehicle Active Noise-Control System Based on an Adaptive Step Size Algorithm
## 1 Introduction  
At present, the NVH performance of vehicles is receiving a great deal of attention, and there is an increasing emphasis on noise reduction. The car's interior noise in low-speed driving conditions mainly comes from the car and the impact of the pavement caused by vibration, due to acoustic transfer characteristics, traditional sound absorption, and vibration damping; while noise processing, such as passive noise reduction patterns, has good attenuation in the case of high-frequency noise [1; 2; 3], low-frequency noise will pass more easily through the sound insulation material to the human ear. In this case, traditional passive noise reduction has been unable to meet the needs of automobile users for noise reduction performance. Because active noise reduction has a good attenuation ability for low-frequency noise, active noise control systems in vehicles have become a hot research topic. The principle of active noise reduction is to form a quiet area in the local space via the superposition of two opposite sound waves, thus achieving the effect of noise reduction [4; 5]. Because active noise control has a good effect on low-frequency noise, many researchers have studied active noise reduction technology in vehicles. [PERSON] et al. [6] developed a prototype ANC system and tested it on a real vehicle. The results showed that the system reduced the roar by more than 10 decibels. [PERSON] et al. proposed a control method for a time-varying fundamental frequency harmonic interference system, provideda non-adaptive method, and gave the results of the real-time measurement of automotive engine vibration by using an active control system, which showed that the noise in the passenger compartment of the vehicle was reduced [7]. [PERSON] et al. [8] proposed a new low-frequency road noise ANC control algorithm, enabling it to be combined with an engine roar noise ANC. The newly developed system is the world's first commercial ANC and is used in sport utility vehicles and sedan models. [PERSON] et al. [9] established an adaptive active noise control strategy for vehicle interiors based on the FxLMS algorithm. The core circuit module of an active noise controller was designed, including the noise signal amplifier module, the main control unit, the audio power amplifier module, and the power module. The hardware of the controller was developed and the control software system was written. By using this system, the low-frequency noise heard by the left ear of the co-driver can be controlled under a steady state; the noise reduction amounts are 8.5 dB and 10.2 dB, respectively. [PERSON] et al. [10] proposed an MExLMS algorithm, combining the threshold of the reference signal and the error signal path to control impact road noise, and established a coupled vehicle system model, based on spectral substructure technology, to simulate the pulsed internal sound caused by road roughness. Numerical simulation results showed that the ANC system can deal with internal collision noise effectively. [PERSON] et al. [11] proposed a CSFxLMS algorithm that minimizes the influence of dynamic characteristics in different reference channels by introducing self-regulating parameters in each reference signal path. The simulation results show that the performance of the CSFxLMS algorithm is significantly better than the traditional FxLMS algorithm, and a reduction of about 5 dBA in the driver's ear position can be achieved. [PERSON] et al. [12] studied a multi-channel vehicle-wide broadband active noise control controller and proposed a practical non-causal inversion method for non-minimum phase secondary paths. The proposed controller can be used as an accurate predictor to estimate the maximum noise reduction that can be achieved. The authors verified the proposed causal optimal controller with measured data, and the results show that the proposed algorithm is superior to traditional algorithms and achieves significant broadband noise reduction in time-invariant systems. [PERSON] et al.