Research On The Active Control Method Of Noise Inside Vehicle Based On Sound Quality

With the rapid development of automobile industry and the improvement of people’s living standards in China, the requirements for the car ride comfort are also increasing. Excessive noise inside the vehicle will not only reduce the ride comfort, but also increase the driver fatigue. Therefore, the interior noise control of car is attracting the increasing attention from the vehicle and parts manufacturers. Along with the development trend of fuel economy and lightweight bodywork of automobile, the low-frequency noise issue will become more prominent. Active noise control method has the advantage for low-frequency noise without big changes to the original structure. Hence, it will have important application value and significance to carry out the study of active noise control inside the vehicles. Furthermore, the researchers need to consider not only the reduction of A-weighted sound pressure level in studying the noise control, but also the improvement of sound quality more seriously. In this paper, the study of active interior noise control method based on sound quality of the vehicle aims to combine the two aspects. It will take into account the influence of sound quality evaluation methods on the noise reduction effects of the control system in the design of active control system, in order to reduce the noise level subjectively perceived by passengers and improve the product quality. The main contents are as follows:1. Study on the design method of residual error shaping filter for active noise control system in consideration of sound qualityBased on FELMS (Filtered-Error Least-Mean-Square) algorithm, high-pass FIR (Finite Impulse Response) filter is used as the residual filter of active system and its design method is studied. The active sound quality control system is simulated by taking loudness control for example. For the noise sources with different spectrum characteristics, the residual error shaping filter of control system will have different cutoff frequencies, decay amount and transition bandwidth to gain minimum loudness. The speech intelligibility with different speech levels inside the vehicle is studied, and the enhancement of speech intelligibility with FELMS and FXLMS (Filtered-X Least-Mean-Square) algorithms is compared as the noise is actively controlled. The results show that FELMS algorithm can gain better effect on noise reduction than FXLMS algorithm by designing an approriate residual error shaping filter.2. Study on the active noise control method based on EMD (Empirical Mode Decomposition) and loudness controlSeeing that the residual error shaping filter of active sound quality control with FELMS algorithm is fixed in previous studies, the active noise control method based on EMD and loudness control is proposed. Firstly, it uses EMD method to decompose the multi-band noise signal adaptively, and calculates the loudness of each IMF component. Secondly, the residual error shaping filter is designed according to the loudness and frequency spectrum of IMF components so as to identify the characteristics of noise source and realize the shaping filter design automatically.3. Study on secondary source modeling method based on analogue circuits of electrical, mechanical and acoustical systemsThe modeling method of secondary sound source of active noise control system based on analogue circuits of electrical, mechanical and acoustical systems is proposed, and the electrical mechanical and acoustical coupling equations are established. The equations are solved by forward Euler method, and the time-domain iterative model of secondary sound source is deduced. By incorporating such a model into adaptive active noise control system with FXLMS algorithm as an example, the influence of secondary sound source model on the convergence range and noise reduction of control system is analyzed by simulation.4. Nonlinearity modeling of secondary sound source and effect analysisThe main nonlinear factors of secondary sound source are described, and nonlinear time-domain model is created by taking the nonlinearity of loudspeaker compliance, force factor and coil inductance into account based on analogue circuits of electrical mechanical and acoustical systems. The compliance, force factor and coil inductance of two types of speakers with different size are measured, and then the harmonic distortion is measured and simulated. The results show that the established nonlinear model of the secondary sound source is feasible in the lower frequency range as the amplitude of input signal is large. The nonlinear model is introduced into adaptive active noise control system, and active control of pure tones with FXLMS algorithm is simulated. The results show that the amount of noise reduction by the control system with nonlinear secondary sound source model is much less than the one with linear model, and the magnitude of nonlinearity will have big influence on the noise reduction of control system.5. Experimental study on active noise control inside vehicleThe interior noise and vibration on suspension of the vehicle are measured under the running conditions of constant speed, accelerating and idling. The active noise control inside the vehicle under different conditions is simulated by using the measured accelerations and transfer functions from the car door loudspeaker to the passenger ears as reference signals and transfer functions of secondary path respectively, and the improvements of sound quality achieved by FXLMS and FELMS algorithms are compared. The noise and vibration of automobile air-condition system and engine cooling fan are measured, and the active sound quality control and distribution of reference sensors are studied. The results show that the control system will have better performance for noise reduction as the reference microphone is laid near the cooling fan or reference accelerometer is laid on the structure near the outlet of air-conditioner. The interior noise of vehicle caused by window lift system is also measured, and the active sound quality control is simulated. The results show that the low-frequency loudness can be reduced and the comfort can be improved. Consequently, such a control system will be beneficial for the solving of booming noise problem inside the vehicle caused by the window lift system.