本文主要目的在於提供不同於過去主動式噪音控制之新概念並落實，在過去主動式噪音控制理論多為LMS演算法(Least Mean Square Method)搭配FIR濾波器(Finite Impulse Response)或是IIR(Infinite Impulse Response)作為控制器，其優點在於可控制寬頻噪音，但本文中所探討噪音對象則為低頻具連續性噪音，由於連續噪音具有單調性與週期性故有容易預測之特性。 本文中數位控制器設計主要概念為利用快速傅立葉轉換(Fast Fourier Translate, FFT) 尋找出空間噪音中最低基頻載波即第一主頻，輔以交互相關分析(Cross Correlation)分析噪音源與其下游受控噪音相位後發出另一反相位聲波，藉由抵消基頻載波擾動以收控制噪音之效果。 The goal of this study is to propose a new method of the implementation of Active Noise Control. People usually use Least Mean Square algorithm (LMS), Finite Impulse Response filter (FIR), or Infinite Impulse Response filter (IIR) as controlling means to reduce the wide band noise. In this study, it is targeting at low frequency, narrow band and continuous humming noise. The main procedures applied in the controller include using Fast Fourier Transformation to find out the dominant frequency of noise and using Cross Correlation to adjust the phase lag of the output sound signal according to the incoming one. The signal with opposite phase relative to the source of the noise is output to drive the anti-sound speaker. Waves from the speaker can then cancel out and then minimize the noise.
