The moving coil transducer’s tendency to generate DC displacement and unstable rest position increases in smaller loudspeakers, which have less energy and hardware resources. A nonlinear motor structure optimized for highest force factor at the rest position provides maximum overall efficiency for common audio signals having bell-shaped probability density function of the voice coil displacement. A new control technique for electrodynamic transducers is presented that stabilizes the voice coil position, compensates for nonlinear distortion, and generates a desired transfer response by preprocessing the electrical input signal. The control law is derived from transducer modeling using lumped elements and identifies all free parameters of the model by monitoring the electrical signals at the transducer terminals. Although the adaptive control algorithm has been illustrated for moving coil transducers, the same approach can also be applied to other transduction structures such as the balance armature transducer in hearing aids and in-ear phones.
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