Observer-based feedback linearization of dynamic loudspeakers with Ac amplifiers

For a reduction of nonlinear distortion produced by a dynamic loudspeaker, there exists a variety of approaches, one of them using the known principle of exact input-output linearization. In combination with a discrete state-space observer, this approach can successfully be applied as long as the amplifier driving the loudspeaker is dc-coupled. This paper discusses how ac amplifiers can be used in this context. It will be shown that an exact linearization is in general not possible with ac amplifiers due to insufficient stability of the feedback system. Two approaches will be presented that abandon the pursuit of an exact linearization in favor of stability and yield satisfactory results when implemented on a floating-point digital signal processor.