Subharmonics in loudspeakers without internal resonance
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摘要: 研究了驱动频率低于扬声器辐射体薄壳轴对称模态最低固有频率的扬声器1/2分谐波失真。采用以位敏探测器作为光电传感器的激光三角法实验观测扬声器振膜的振动位移和模态,确定了参与的非轴对称模态的周向波数。采用多尺度法求解了扬声器的非线性模态方程。给出了扬声器分谐波的阈值电压公式。结果表明扬声器辐射体薄壳的分谐波失真源于直接激励的轴对称模态耦合激发了非轴对称模态的振动,这种耦合激励表现为参数激励。增大扬声器振膜材料的损耗因子、杨氏模量和厚度可提高产生分谐波的阈值电压。Abstract: The 1/2 subharmonics distortion in a direct radiation loudspeaker is investigated when the driven frequency is lower than the lowest nature frequency associated with the axisymmetric mode of the loudspeaker shell.The laser triangulation method based on the PSD(Position Sensitive Detector) is used to measure the vibrations and modes of the loudspeaker shell.With the participant asymmetric mode determined,the method of multiple scales is then used to obtain the first-order approximations to the nonlinear modal equations for the loudspeaker shell.The formula of the threshold voltage of the subharmonics is given.The results show that the subharmonics in the loudspeaker are caused by the asymmetric mode excited parametrically by the axisymmetric vibration.Increasing the loss factor,the Young's modulus of the loudspeaker shell material or the shell thickness can increase the threshold voltage of the subharmonics occurrence.
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