The Transient Magnetic Behaviour of Loudspeaker Motors
Magneto-static Finite Element Methods have been applied to the design of loudspeaker motors for some time. Advances in both hardware and software present the opportunity of extending our knowledge about the detailed electro-magnetic behaviour of loudspeaker motors. In particular by coupling a lumped-element kinematic model to a transient-magnetic finite element model, the dynamic behaviour of a loudspeaker voice coil may be calculated for an arbitrary electrical input. This motion includes components due to transduction non-linearities such as flux-modulation, eddy currents, and force factor profile. A great advantage of this technique is that the results show the distribution of eddy currents throughout the structure allowing their display and analysis. Furthermore, by calculating the motion of a loudspeaker voice coil for a sinusoidal input, the harmonic distortion of the transduction mechanism may be calculated at any chosen level and frequency. Preliminary results obtained by using transient-magnetic FEM with kinematics are presented for a new motor structure to illustrate some of the benefits and current limitations of this technique.
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