Research Of Peak Noise Caused By Time Delay Of The Anti-Noise Source

There is growing attention to noise pollution nowadays. The most commentmethods to control the noise are sound-absorbing process, sound insulation, noisedeadener, vibration isolation, damping vibration attenuation and so on. These passivenoise control methods are effective for high frequency noise but are not very wellways to reduce low frequency noise. In the noise composition of the city, thepercentage of low frequency noise is increasing rapidly and low frequency noise is themost difficult to eliminate. ANC(Active Noise Control)technology has obviousadvantage of processing this kind of noise. In recent years, extensive study isconducted for low frequency noise. Theoretical research is rather mature but slowprogress is made in the practical application. Usually, some applications that someacoustic experts spend a lot of time and energy working out are effective for a certainkind of noise but are not applicable or not satisfactory for another kind of noise. As aresult, there has always been a problem in application. Problems in the application ofactive noise control technology have always been difficult and hot points in currentresearch of noise control. From the points of view for practical uses, this paper studiesthe method of suppressing the peak noise caused by the time delay of the anti-noisesource and analyzes a potential problem in the application of active noise controltechnology.This paper introduces briefly the effects of low frequency noise and peak noiseand discusses the develop course, domestic and foreign research condition, basicprinciples, ideas and processes of ANC and analyses the mainly links which delay inthe process of ANC exists in and illustrates that the existence of delay is inevitable. Italso demonstrates that the sound pressure magnitude of peak noise is large and theenergy of peak noise could not be neglected. MATLAB is used in the simulation. Theresearch object is random low frequency noise signal and the frequency range is set as20～500Hz. Real time property is the key of ANC. In the process of research, ANCunder real time condition is simulated by using simple principle firstly. Theeffectiveness indicates the feasibility of this principle. The same principle is used toincrease the simulation time delay and to do the simulation analysis of the noisecontrol effect when the simulation frequency is different under two conditions: a.periodic signal with different simulation time delay; b. non-periodic signal with different simulation time delay. It shows that the peak noise is inevitable, indicates thecondition of producing the peak noise and supposes a analog control method ofsuppressing the peak. Finally, the effectiveness of suppressing the peak noise usinganalog control has been tested and verified by digital simulation results. Simpleexperiments were conducted to validate the effects on reducing the noise by ANC andthe existence of peak noise caused by time delay of anti-noise source.Simulations and experiments show that time delay is inevitable in ANC process,real time conditions cannot be gotten, time delay of the anti-noise source willinfluence the effects of noise attenuation, and that peak noise whose amplitude islarger than that of original noise signal will appear. Peak noise is formed when thephases of the original noise signal and anti-noise signal are the same. In the process ofANC, peak noise could be effectively controlled by fuzzy control which has the stepof comparing the amplitude and phase.