Research On Active Noise Reduction System In Small Space

As one of the four major environmental problems in the world,noise pollution affects people's normal life and work in varying degrees.For noise pollution,the soundproof earmuffs are generally used to block the sound wave path to achieve noise reduction in the small space between the human ear and the earmuff cavity,which can be called small space noise reduction.The traditional physical noise reduction method has a good noise reduction effect on high-frequency noise,but the noise reduction effect is not good for the low-frequency band below 700 Hz.Active Noise Control(ANC)achieves a good noise reduction effect on low-frequency noise by sending out an anti-noise to interference with original noise.The main work accomplished by this article includes:Firstly,the paper studies the basic principles of analog active noise reduction,common topologies,the adaptive filter principle of digital active noise reduction and the adaptive filtering algorithm of FXLMS are also studied respectively for the two kinds of noise reduction schemes of analog and digital.Secondly this paper studies the analog active noise reduction scheme represented by AS3415 chip.Including: hardware structure of the active noise reduction chip,noise reduction principle,prototype acoustic performance testing steps and feedback filter network design and simulation.the AS3415 demonstration board and ordinary headphones as the experimental platform for noise reduction test.The analog noise reduction scheme has a certain noise reduction effect to the frequency noise below 700 Hz and the noise reduction effect near 100 Hz reaches 10 dB.Then the digital scheme introduces the feedforward active noise reduction technology based on the Filter-X Least Mean Square(FXLMS)algorithm,combines with the peripheral hardware circuit to achieve the function of active noise control.Compared with the passive noise reduction method,the common music headphones with digital noise reduction algorithm can reduce the noise reduction of 200 Hz by 24 dB and the pink noise of 100-1000 Hz by 12.2dB.When the passive noise reduction platform change to professional noise headset,the single-frequency noise for 100 Hz noise reduction increased by 27 dB,100-1000 Hz pink noise reduction noise increased by 8dB.Through introducing the passive noise reduction model,it can improve the broadband pink noise reduction to 12 dB.This paper discusses the noise reduction principle,system structure and specific implementation steps of the two active noise reduction schemes for analog and digital,which are helpful to the design of an active noise reduction ear muffler with high versatility and active noise reduction performance.