| Summary: | 碩士 === 國立臺灣大學 === 造船工程學系 === 81 === In noise control engineerihg , the passive control techni -que
is always popularly used to improve noise problem . And the
above passive noise control technique is almost using the
combination of panels with absorbing materials to protect the
transmission in duct by changing its cross-section . Generally
, passive noise control technique doesn't have good control
effectiveness on noise at low frequency and also appears very
uneconomically . For the case of rectangular aperture , using
absorbing material also can greatly reduce high-frequency noise
. But it still can't provide an effective control method to low
-frequency noise . Therefore , this paper would like to
concentrate the study of adaptive control system design and it'
s effectiveness to noise control on sound transmission through
apertures at low frequency . In discussing the above adaptive
control system , it's main acoustic logic is using a FIR filter
with adaptively adjusting it's parameters to produce an output
signal that will make controllable sources to generate an
acoustic filed to pro -tect the noise tranemission being
controlled . Hence this study would like to set up an
experiment of active control on pure tonal noise of low
frequency by matching error signal transmitting from monitoring
microphone after aperture with the parametric operation on
system by least square method . Finally , the results of active
control experiment on noise in aperture shows that the
greastest acoustic reduction of noise transmission in aperture
by 15 decibels would be obtained when the adaptive control
technique building in this paper is used .
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