Error Correction of Loudspeakers: a study of Loudspeaker Design supported by Digital Signal Processing

Throughout this thesis, the topic of electrodynamic loudspeaker unit design and modelling are reviewed. The research behind this project has been to study loudspeaker design, based on new possibilities introduced by including digital signal processing, and thereby achieving more freedom in loudspeaker unit design.

This freedom can be used for efficiency improvements where different loudspeaker design cases show design opportunities. Optimization by size and efficiency, instead of flat frequency response and linearity, is the basis of the loudspeaker efficiency designs studied.

In the project, a nonlinear loudspeaker model has been used for both power consumption and distortion simulations. The nonlinear model has been improved by adding time varying suspension behaviour. The basic improvement is a heating phenomenon of the suspension. The addition to the model improves the loudspeaker model performance at low frequencies.

A model based controller has been constructed, where a simulation study including a measurement series of parameter drift in the loudspeaker units has been included. This led to the conclusion that a parameter update of the loudspeaker parameters is needed during operation of a nonlinear feed forward controller.

System identification is used for tracking the loudspeaker parameters. Different system identification methods are reviewed, and the investigations ends with a simple FIR based algorithm. Finally, the ­parameter tracking system is tested with music signals on a 6½ inch bass-mid range loudspeaker unit.

The knowledge of loudspeaker construction and efficiency is used for the analysis of Digital Loudspeaker Arrays (DLA). This work is made in cooperation with the University of Patras, where DLA is a focus area. This project focuses on efficiency and transducer limitations of the DLA. Performance analysis of DLA is the name of the joint research project. Parts from this project are presented in this thesis.