Modeling and Compensation of Nonlinear Distortion in High Efficient Electrodynamic Loudspeakers

Loudspeakers transform electrical energy into acoustic waves but most of the electrical energy is lost as heat. It is possible to increase the electro-acoustic efficiency by changing the electrical, mechanical or acoustical design of the loudspeaker but with these changes come unwanted side effects. An efficient loudspeaker exhibits strongly nonlinear behavior, but the nonlinear effects can be reduced by the means of implementing an algorithm on a digital signal processor. This is of great interest for Axis Communications since it makes it possible to increase the efficiency in their products without loss of sound quality. The purpose of this thesis was to investigate nonlinear distortion in high efficient electrodynamic loudspeakers using a simulation software, COMSOL Multiphysics, and to model the nonlinear response of the loudspeaker behavior. The simulations were conducted in order to get an understanding of the nonlinear behavior but also to estimate data for the theoretical model. Further, a nonlinear model describing the voice coil excursion was investigated with the purpose of constructing a nonlinear filter able to reduce nonlinear distortion. The result of the simulation showed it was possible to estimate the force factor as a function of voice coil displacement and that it also should be possible, according to the magnetic fields and streamlines, to obtain the function that describes the voice coil inductance from the same simulation of the loudspeaker. The numerical implementation of the voice coil excursion showed the voice coil was operating in the wrong domain when it was driven with a real input signal. Hence, the Volterra series need further work before a nonlinear filter can be derived