扬声器辐射体旋转薄壳的非线性振动方程

推导了扬声器辐射体旋转薄壳的离散非线性振动方程。从虚功原理出发,选用扬声器辐射体旋转薄壳的本征模态对连续体进行离散。薄壳的几何非线性采用Sanders非线性薄壳理论的应变一位移关系。方程系数由有限元方法确定。方程表明轴对称模态由驱动力直接激励,非轴对称模态由轴对称模态非线性耦合激励,该耦合激励表现为参数激励。方程揭示了扬声器非线性失真的机制,可用于分析扬声器辐射体薄壳非线性引起的谐波失真、分谐波失真和互调失真。      

有内共振时的扬声器分谐波和混沌

研究了当轴对称模态由驱动力共振激发,并且轴对称模态和非轴对称模态存在2:1内共振时的扬声器辐射体薄壳的分谐波和昆沌。采用多尺度法分析了非线性模态方程的稳态解及其稳定性,由此进一步确定了驱动频率和驱动力平面上的分岔集。给出了所考虑情形下扬声器分谐波的阈值电压公式,该阈值电压低于无内共振时的阈值电压。除出现非轴对称模态的1/2分谐波振动外,2个模态的振幅经Hopf分岔后作极限环运动,并经倍周期分岔进入混沌运动。混沌出现是由于2个模态间能量的强烈交换。理论结果和实验结果基本吻合,该一致性表明了所建扬声器非线性薄壳模型的正确性。      

扬声器辐射体旋转薄壳的谐波失真

研究了扬声器辐射体旋转薄壳几何非线性引起的谐波失真。采用摄动法和有限元法确定了2次和3次谐波振型,计算了薄壳材料参数和几何参数对谐波失真的影响。结果表明扬声器薄壳谐波失真的机制是分割振动模态的基波共振和超谐波共振,以基波共振为主。采用高阻尼、大杨氏模量和低密度的振膜材料可以降低振膜谐波失真;厚度对谐波失真的峰值影响不大;锥壳半顶角过大,可使3次谐波明显增大。      

用激光自混合干涉测量扬声器的Q值

用激光自混合干涉方法测量扬声器振动,从扬声器振动引起的自混合干涉信号测量扬声器振动速率.由正弦波激振扬声器测量振速的幅频特性曲线,谐波中包含扬声器谐振频率的方波激振扬声器测量振速衰减曲线,分别按谐振法和衰减法测量得到扬声器的品质因数约13.3和10.2.由于方波激励时扬声器有谐波振动成分,由方波激励获得的衰减曲线测量得...     

扬声器的分谐波失真

扬声器在振动时可发生分谐波失真，这是人们已发现的事[1]．本文给出了扬声器分谐波现象的实例，对其产生机制作了简委的说明，并且指出了分谐波的动态变化特性．通过合成分谐波的方法对分谐波的所感进行了主观试听评价．实验结果发现，分谐波比高次谐波更易为人耳察觉，对音高、音质的影响很明显，甚至到破坏的程度．     

微型扬声器摆动模态对其辐射声场的影响*

与传统电动式扬声器单元相比,微型扬声器单元由于缺少定位支片等部件,更容易受到摆动模态的影响。该文利用激光传感器采集微型扬声器单元振膜各点振动位移,通过理论计算,从辐射声压级、辐射指向性等角度探究矩形微型扬声器单元摆动模态对其辐射声场的影响。经过研究发现,摆动模态会造成微型扬声器单元频响凹陷、中低频存在指向性等现象,对其辐射声场产生明显的影响。     

扬声器异常音的快速检测方法及其实验研究

提出了一种对扬声器声响应中的低阶次谐波失真与高阶次谐波失真和进行综合分析的方法,以实现对扬声器异常音的快速检测。文章分析了扬声器异常音的时域和频域特征,并对人耳听测异常音的机理进行了讨论。通过对扬声器系统Volterra建模并选择连续对数扫频信号作为激励信号,推导出了该模型在此激励下的响应表达式.该表达式揭示了提取各阶冲激响应的方法,由该表达式给出一种可以快速提取各阶次谐波失真的跟踪滤波器,以实现对扬声器异常音的检测。实验室测试和多次工厂生产线测试初步验证了该方法的准确性、快速性和可行性。      

水下任意形旋转薄壳振动和辐射声的时域研究

本文通过采用DAA2方法,有限元模态展开和直接积分混合方法以及Kirchhoff推迟势的边界元解法在时域上对水下任意形旋转薄壳振动和辐射声进行研究。以水下椭球壳的端部轴对称激励问题为例,对力源的时间函数分别为单频填充脉冲和δ脉冲两种情况给出了一些典型的数值计算结果和实验结果,并进行了讨论。     

振膜与音圈粘结间隙对高频截止的影响*

利用声学理论及Comsol仿真对电动式高音扬声器声压级高频进行分析,重点研究了高音振膜与音圈的粘结状态对声压级高频截止的影响。根据实例分析,当音圈与振膜之间的粘结间隙被中心胶填充时,Klippel测试的声压级高频提前截止。通过对中心胶粘结位置相关的类比线路图分析可知,扬声器高频截止频率主要受振膜和中心胶的刚性影响,当中心胶粘结位置存在间隙时,因中心胶材料与骨架材料比模量的差异,Cglue变大,此时整体刚性变小,会使振动能量由音圈骨架传递到振膜材料时的传递速率受到削减,表现为高频截止频率降低。Comsol仿真分析表明,音圈骨架与振膜粘结位置存在间隙时,高频振动模态发生弯曲,影响振动能量的传递,高频提前截止,与实例分析的结果一致。     

双激励纵弯耦合宽带复合棒水声换能器

为研究进一步拓宽双激励复合棒水声换能器的工作带宽方法。利用等效电路法和有限元方法研究了双激励换能器的振动模态,分析了中间质量块的材料、长度对换能器发射电压响应的影响,提出结合较低工作频段的纵向振动和较高工作频段的纵向振动与径向振动耦合引起的弯曲振动进一步展宽带工作频带的方法。根据优化参数后的仿真模型制作的样品工作频带为14 kHz～47 kHz。采用这种纵弯振动模态耦合的方法可以有效拓宽双激励宽复合棒换能器的工作带宽。     

扬声器锥壳的全频段振动通解

为更好地理解扬声器数值计算结果,解析研究了扬声器锥壳轴对称振动在整个工作频段一致有效的通解,这些解以特殊函数的形式给出。在典型低频段,弯曲解仅表现为边界层效应;在典型转点频段,弯曲解存在于转点的外侧域;在典型高频段,弯曲解覆盖了整个扬声器锥壳。无矩解和弯曲解在转点频段是耦合的,该耦合特性表明在此频段不可能消除分割振动。      

扬声器锥壳的全频段强迫振动解

解析和数值研究了扬声器锥壳全频段的轴对称强迫振动。给出了典型低频段、典型转点频段和典型高频段的显式位移解析解、特征频率方程和轴向导纳表达式。解析结果与数值计算和实验结果结果非常吻合。在典型低频段,振动完全是纵波型的。在典型转点频段,全域的纵波运动和转点外侧域的横波运动共存,谐振和反谐振频率方程相应呈现出无矩解和弯曲解的耦合特性。在典型高频段,全域的纵波运动和横波运动互相独立,相应出现2组独立的纵波和横波固有频率。      

Influence of initial geometrical imperfections on vibrations of axially compressed stiffened cylindrical shells

The vibrations of stiffened cylindrical shells having axisymmetric or asymmetric initial geometrical imperfections and axial preload are analyzed. The analysis is based on a solution of the von Kárman-Donnell non-linear shell equations, an “exact” solution of the compatibility equation, and a first order approximation by the Galerkin method of the equilibrium equation. The stiffeners are closely spaced and “smeared” stiffener theory is employed. The results of an extensive parametric study carried out on shells similar to those used in vibration and buckling tests at the Technion show that stiffening of the shell will lower the imperfection-sensitivity of its free vibrations, but the decrease depends on the type of stiffening (stringers or rings), the mode shapes of the vibration and the imperfection, the stiffener strength and eccentricity. The imperfection-sensitivity decrease, caused by the stiffeners, is greater for vibration mode shapes with high imperfection-sensitivity than for other vibration mode shapes. The sensitivity differences between stringer and ring-stiffened shells depend especially on the vibration and the imperfection mode shapes, and on their coupling. Small imperfections change the natural frequencies of stiffened shells in the same directions as for isotropic shells, but to a smaller extent. The frequency dependence on the external load is also strongly affected by the imperfection mode shape. The results correlate well with earlier ones for isotropic shells.     

Effect of heterogeneity on the axisymmetric vibrations of cylindrical shells

The influence of large heterogeneity on the axisymmetric vibration characteristics of thin, composite cylindrical shells is studied, both analytically and numerically. In the neighborhood of the axisymmetric breathing mode, frequency spectra for shells of infinite and finite length are shown to be influenced qualitatively as well as quantitatively by large deviations from material and geometric symmetry in layer arrangement. A study of mode coupling in a semi-infinite shell is made for both end modes and modes with stationary frequency with real finite wave number, the latter being uniquely generated by a special class of heterogeneity. In each case, analytical estimates are given for frequencies, wave numbers, and modal amplitudes as functions of material and geometric properties of the shell.     

Transient modal radiation of axisymmetric sources: Application to loudspeakers

The present study proposes a transient model of the acoustic radiation of axisymmetric structures. The pressure field is approximated by the Rayleigh integral corresponding to a monopole source distribution over the non-planar vibrating surface. The displacement field is expanded on the linear modes of the structure and a change of variables in the Rayleigh integral is then proposed in the case of a monotonic profile function to compute the Spatial Impulse Response associated to each mode of vibration efficiently. The results are compared to the formulation obtained in the case of planar and spherical sources. The method of calculation is then derived in the case of a typical loudspeaker profile (association of a truncated cone with a spherical cap). Finally, the present approach is used to estimate the nonlinear radiation pattern of a prototype loudspeaker and predictions are compared to measurements in anechoic room.     

Free vibration study of layered cylindrical shells by collocation with splines

The free vibration of circular cylindrical thin shells, made up of uniform layers of isotropic or specially orthotropic materials, is studied using point collocation method and employing spline function approximations. The equations of motion for the shell are derived by extending Love's first approximation theory. Assuming the solution in a separable form a system of coupled differential equations, in the longitudinal, circumferential and transverse displacement functions, is obtained. These functions are approximated by Bickley-type splines of suitable orders. The process of point collocation with suitable boundary conditions results in a generalized eigenvalue problem from which the values of a frequency parameter and the corresponding mode shapes of vibration, for specified values of the other parameters, are obtained. Two types of boundary conditions and four types of layers are considered. The effect of neglecting the coupling between the flexural and extensional displacements is analysed. The influences of the relative layer thickness, a length parameter and a total thickness parameter on the frequencies are studied. Both axisymmetric and asymmetric vibrations are investigated. The effect of the circumferential node number on the vibrational behaviour of the shell is also analysed.     

Theory of spatial subharmonic instability under hologram recording in a photorefractive crystal with applied AC field

A theory describing threshold conditions for spontaneous generation of spatial subharmonics in a photorefractive crystal with an externally applied square-wave ac voltage is presented. Predicted results are in good agreement with the experimental data.