有源消声系统中的电场的阻抗规律及其应用

运用电力声类比方法，研究有源消声中声源电声阻抗变化规律，首先给出动圈式扬声器总输入电阻抗表达式，并分析了声源辐射阻抗对电阻的影响关系，其次研究了在声抑制和声吸收两种消声状态下，次级源电阻抗的变化规律，并推导了换能器输入电压与输出振速间的关系；最后设计了交流电桥，实际测量两种消声状态下，若干频率时次级扬声器电阻抗规律，得到了与理论分析一致的结果。

An Impedance-Based Control System and its Application in Active Noise Control, Part Ⅱ:Electro-Impedance Theory and Measurement

To our best knowledge, there still does not exist any impedance based noise control system made or designed in China. The first part of our research on such a control system was reported in Ref.5] . In our experimental research, we needed the general input electro impedance for a coil driven loudspeaker and we derived eq.(1) as its expression according to well known principles. In section 2, we discussed in much detail the variation of the input electro impedance with radiation impedance for two noise reduction strategies; the actual variations are shown in Fig.2. In section 3, we discussed the conversion of the problem of finding the optimal strength of a sound source into that of finding the optimal input electro impedance for two noise reduction strategies; the actual conversion factors for amplitude and phase respectively can be taken from curves in Fig.4. Finally, we measured the input electro impedance of the secondary loudspeaker for two noise reduction strategies in a semi anechoic chamber. Fig.6 shows the measured values which agree fairly well with theoretical analysis.