臺灣博碩士論文加值系統

本論文針對一維方形管道聲場，受主動控制穩定消音的前題下，進行
聲源的音響阻抗量測與分析，以說明第二聲源在主動控制狀態下，對第一
聲源所造成的影響；並且實際量測主動控制前後兩音源的音壓大小值、相
位關係值以及其傳播的聲功率，分別與聲學的理論公式進行比對，以驗證
本論文所引用之量測法的可行性及準確性。 實驗中以轉移函數法求得
噪音源振動板的反射係數，藉此實際求得之係數代入理論公式中，以期更
符合實際趨勢，其中包括兩音源的強度關係及控制前後的阻抗變化，皆與
噪音源振動板的反射係數存在密切關係。 真實的主動控制狀態下，聲
壓隨時間變化的不穩定特性，有礙於聲場中音響阻抗之量測，故本文採取
以手調兩聲源音壓之大小值及相位值方式，模擬主動控制的穩定狀態，提
高實驗的正確性。

Researching the physical property in the square duct of the
active noisecontrol system. Include the impedance of the primary
and secondary source with and without active noise control.
Using Helmholtz resonator measures the impedance of the primary
source and secondary source in the one dimension square duct as
the ANC system isturned on and turned off. Considering the
reflecting effect produced by the vibrating membrane of the
primary source disturbers the sound field in a square duct.
Using "Transfer Function Method" measures the reflection
coefficient of the membrane and substitutes the coefficient into
the sound field theory of square duct acquired by "image
method". Then we can approach the experimentaland the
theoretical impedance of sources in the duct. The resistance of
the primary and the secondary source is respectively 5 and 4
percentage of the original resistance before ANC as the
downstream pressure is reduced at least 40 dB in the duct. Then
we can say that the secondary source in an ANC system is a sound
absorber or a sound reflector which makers the sound pressure in
the downstream of duct would be reduced.