| Summary: | 碩士 === 國立臺灣大學 === 土木工程研究所 === 82 === We use adaptive control to attenuate the noise at a point in
three dimensional space. The adaptive algorithm adopted is the
normalized least mean square (NLMS) method. The signal detected
by a microphone is used to estimate the demanded output of the
speaker which plays the role of a controller, and the system
parameter is then updated with the aid of the error signal
detected by another microphone, usually called the error
microphone. The system is modeled as either a finite impulse
response (FIR) filter or an infinite impulse response (IIR)
filter. We suppose the property of the system is indefinite,
and deduce an adaptive FIR control rule and an adaptive IIR
control rule. A geometric point of view is employed herein to
see the convergent behavior of the NLMS algorithm, including
the convergence of the successive estimated values of the
system parameter and the estimated errors in the cases where
the output signal of the system is under the influence of
noise. According to the theory deduced and the results of
numerical simulations and lab experiments, the wideband signal
is found most suited to identify the impulse response of the
system considered. Our experimental results show that the
effect of noise control using the FIR model is better than that
using the IIR model.
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