The Research Of Adapted Active Noise Control Theory In Vehicle

To reduce the noise in vehicle,is the problem that many countries' Government and the vehicles Manufacturer concern about together.Nowdays the noise control technology has become more mature,and is widely used in many fields.However, the wavelength of low-frequency noise is so long,which can easily get over the sound-absorbing material.Therefore, the Active Noise Control (ANC) technology is generally used to the control the low-frequency noise.With the purpose of noise reduction,ANC is a technology that a sub-acoustic signal is produced artificially and purposefully to control the primary acoustic signal in a designated area.It is based on the principle that two sound waves superposition to counteract.If the sub-acoustic signal has the amplitude equaled to the primary acoustic signal,and the phase contrasted with the primary acoustic signal,it can counteract the primary acoustic signal to reach the purpose of noise reduction. with the rapidly development of electronic technology and control theory as well as the practical application of digital signal processing,Adaptive filtering technology is used to Active Noise Control system.The noise Control system could automaticly select control parameters, according to continuously track the variety of source of the noise and environmental parameters.So it can keep on the best working conditions.Until AANC system is formed,active noise control technology become a more practical means of Noise Control.This article is a preliminary study of ANNC against the particular space in vehicle.To begin with,basal conception of noise signal analysis and processing is introduced in this paper.Also Acoustic transmission formula on a enclosed space is gained. regarding acoustic model in vehicle as a car shell and internal air fluid coupling model,we generate meshes and build up a model.In front of the model where engine should be,we lay a point source with 10Pa sound pressure,200Hz excitation frequency and 0 initial phase.then the situation of the sound field in vehicle is simulated.The result validate that sound pressure keeps moving up and down with away from the sound source because of the interaction of standing waves.Next we lay one secondary source and two secondary sources severally on the position of back seats in vehicle.Then the sound field after superposition is simulated. Sound pressure slicing map and pressure curve is drawn out.From the pictures,it can be seen that noises in most of the space ,especially noises on the rear seat passenger's position,is obviously controlled.Active Noise Control Theory is observablly proved.Adaptive Filter is the best filter abased on Least Mean Square principle.The theory of adaptive Filter is discussed in this paper. Then we derived Least Mean Square(LMS)algorithm which gain recursive Formula of Weight vector by the steepest descent method.Steady-state conditions of the algorithm has been analysed in the paper.The value of the convergence coefficient has also been discussed here.The main study in this article is Single Channel feedforward ANNC system.The model of the system is build up .Filter-XLMS algorithm and its performance is analyzed and discussed.On this basis,Using MATLAB / Simulink as a tool ,ANNC simulation system is created.Block diagram of the adaptive feedforward Active Noise Filter-XLMS Algorithm ,and explanation of component modules in the structure are also given here. In the simulation,the main parameters, the length of filter and the convergence coefficient, which directly impact on the results of noise control,are compared by different values. Considering both speed and effect of convergence,we choose filter length as 32 and convergence coefficient as 0.65.In the project named"the pass noise Identification of accelerated moving vehicle"cooperated by our laboratory and Changchun FAW Group Technology Center,we obtain the noise signals from rear seats positions of car in steady-state conditions. Then noise cancellation is carried out to these noise signals. The original noise signal, target signal, the error signal and signal after noise cancellation come into being. Waveform and frequency spectrum pictures of these signals are drawn out.From these pictures,we analyse the low-frequency characteristics of original noise signal,and the process that the filter weights achieve stability from a initial assumption by gradually adapting to the signal.With the Comparison from frequency spectrum picture and 1/3 octave frequency spectrum picture between the original noise signal and the signal after noise cancellation,it's clearly observed that low-frequency noise is reduced commendably. Sound pressure levels of the original noise signal and the signal after noise cancellation are calculated. Finally we get the overall noise reductions of the process.According to the control of the noise signals measured from the car in steady-state conditions, it's clearly observed that Single Channel feedforward ANNC system is very obvious on the effect of low-frequency noise cancellation. The overall noise reductions are from 7dB to 9dB. The purpose of the noise control has been commendably achieved. After the experiments and the simulations, It can be established that the Active Noise Control Model according to Filter - XLMS Algorithm builded in this paper is a more applicable means to the low-frequency noise control in vehicle.