Study On Mechanical And Electrical Nonlinear Parameters Of Loudspeakers

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.