【作者】 夏洁；

【导师】 沈勇；

【作者基本信息】 南京大学 ， 声学， 2012， 硕士

【摘要】 扬声器单元在大信号输入时,由于内在的热学机制和非线性机制,其输出信号会产生畸变。很明显,目前常用的线性模型无法描述扬声器单元的大信号特性,只能局限在小信号范围内。然而,在扬声器单元设计中预测和提高其大信号性能已变得越来越紧迫。现在,无论是专业用的还是家用的,都追求尺寸小、质量轻、成本低但同时效率高、失真小的扬声器单元。急需深入研究以迎接这样的挑战。本文首先引入了扬声器单元的非线性模型,并在模型中考虑了涡流效应的影响(LR-2模型)以及磁阻力。介绍了四个主要的非线性参数Bl(x)、Kms(x)、Le(x)、 Le(i)产生非线性的原因,并阐述了各个参数对最大线性位移Xmax的估算作用。扬声器单元的非线性特征主要表现为以下几个方面：一是幅度压缩；二是产生非线性失真,主要是谐波失真和调制失真；三是音圈位移中产生直流分量。本文以非线性模型为基础,通过数值模拟的方法系统地分析了各大信号参数Bl(x). Kms(x)和Le(x)对上述非线性特征的影响,其结论可以帮助我们诊断扬声器单元的大信号性能。本文的目的是提供一种评估扬声器单元大信号性能的高效方法。为此,本文从幅度压缩、谐波失真、调制失真、位移的直流分量等方面比较了两个实际的扬声器单元的实际测量值和数值模拟值。结果表明两者吻合很好,这说明此数值分析方法可用于评估扬声器单元的大信号性能。更多还原

【Abstract】 For many years linear models have been used for predicting and simulating the loudspeaker behavior. Linear models assume a linear relationship between the input and output for any signal amplitude. However, a real speaker limits and distorts the output at higher amplitudes due to thermal and nonlinear mechanisms inherent in the loudspeakers. Clearly, linear models fail at high amplitudes and are restricted to the small signal domain. However, assessing and improving the large signal performance becomes more and more an issue in loudspeaker design. Professional, multimedia, automotive and hi-fi applications require small, light-weight drivers manufactured at low cost generating the acoustical output at high efficiency and low distortion. New adequate tools are required for mastering the current challenges.The aim of this paper is to describe the non linear behavior of loudspeakers. For this purpose, a nonlinear analytic model has been constructed which takes into account the variations of the small signal parameters and also the effect of eddy current (LR-2). Then the nonlinear mechanism of several dominant large signal parameters——nonlinear force factor Bl(x), nonlinear stiffness Kms(x), inductance of voice coil Le(x,i) are discussed in detail. The method is also presented that how to evalute the maximal (linear) peak diaplacement Xmax by the above three nonlinear parameters.The main effects which are generated by a nonlinear system (e.g loudspeakers) are as follows. The dependency on the amplitude is an indication for nonlinearities inherent in the system. A second nonlinear effect is the generation of additional spectral components which are not in the exciting stimulus. Those components may be interpreted as harmonic and intermodulation distortion and are the basis for traditional measurement techniques. The dynamic generation of a dc-component in the voice coil displacement which shifts the coil out of the gap is also a special symptom generated by the nonlinear system at high amplitude. Thus, in the second part of the paper the relationship between the driver nonlinear parameters and the resulting transfer responses will be discussed in detail to understand complicated effects. A numerical technique will be presented to predict the transfer functions using the identified model. Each nonlinear parameter is described at least by a linear and a quadratic term. The effect of each term is studied separately, as they don’t influence the same kind of frequencies. Both terms considered together result in enhanced effects. Characteristic symptoms are found for nonlinear parameter and presented systematically in a guide for loudspeaker diagnostics.It is the goal of the paper to provide a simple guide for assessing the large signal performance of loudspeakers. In the remaining part of the paper this guide will be applied in the diagnostics of2real loudspeakers. Numerical simulations and experimental investigations are undertaken for validating the loudspeakers. The agreement between measured and predicted responses opens the way for a new kind of loudspeaker diagnostic. Conclusions are drawn for practical work and further research.更多还原