Digital compensation of nonlinear distort ion in loudspeakers

Ideal loudspeakers produce acoustic waves, which are a linear transformation of the electrical input signal. In reality loudspeakers do produce nonlinear distortion as well. This paper presents a method to compensate this distortion in real-time by nonlinear digital signal processing, implemented on a Digital Signal Processor ( i . e . the TMS320C30 DSP). Based on literature, an electrical equivalent circuit of an electrodynamic loudspeaker is developed first, resulting in a linear lumped parameter model. The parameters in this model are matched with the measurements of a selected test loudspeaker. The linear model is extended to include nonlinear effects by developing the parameters as a function of the voice coil excursion of the loudspeaker in a Taylor series expansion. The resulting nonlinear system is described by a Volterra series. Based on this description an inverse circuit is designed for the second order nonlinear distortion. This circuit is implemented in real-time on the DSP, using a high-level design and code generation system (SPW). Simulations and experiment are presented.