Abstract

This thesis treats the problem with nonlinearities in a loudspeaker driver. The hypothesis was: Can the harmonic distortion in a loudspeaker driver be removed using control knowledge? The loudspeaker driver was studied and a mathematical model of a driver was made. The mathematical model was analysed and reduced. To remove the harmonic distortion this thesis analysed the model, and located the nonlinear elements producing the harmonic distortion. A control scheme was presented and designed. The scheme consisted of a controller, a closed loop observer and a adaptive estimator. The controller designed, uses the nonlinear control type feedback linearization. The controller was simulated, and found usefull for reducing the nonlinearities in the driver. The controller had to be sampled with a larger sampling frequency han first assumed in order to completely remove the harmonics. A Kalman filter was developed as a closed loop observer to estimate the non measurable states of the system. The observer was tested, and found sufficient for this project. The adaptive estimator used a set of coefficients obtained from a Klippel Analyzer to extrapolate the parameters. Methods for estimating the nonlinear parameters of the driver are presented. The final simulation with the controller and closed loop observer, showed it was not possible to remove the nonlinearities of the driver, but it was proves possible to reduce them.

Denne afhandling behandler problemet med ulinearitet i en højtaler enhed. Hypotesen er følgenden: Kan de harminiske forstyrrelsen i en højtaler enhed fjernes ved hjælp af viden om kontrol. Enheden er studeret og en matematisk model er analyseret og reduceret. For at fjerne de harmoniske forstyrrelser er modellen i denne afhandling blevet analyseret og fundet de ulineare elementer der laver de harmoniske forstyrrelser. Et kontrol plan er presenteret og designet. Planen består af en kontroller, en lukket sløjfe observator og en adaptiv estimater. Den designede kontroller, bruger ulinear kontrol typen feedback linearisering. Kontrolleren er simuleret og fundet brugbar til at reducere ulineariteten i enheden. Kontrolleren skulle samples med en større samplings frekvens en først forventet, for at helt at kunne fjerne de harmoniske. Et Kalman filter var udviklet som en lukket sløjfe observer for at estimere de tilstande af systemet der ikke er målt. Observeren blev testet og fundet tilstrækkelig til dette projekt. Den adaptive estimater bruger et sæt af koefficienter, fundet ved hjælp af en Klippel Analyzer, til at finde parametrene. Metoder til at estimere de ulineare parameter for en enhed er præsenteret. Den afsluttende simulering med kontroller og lukket sløjfe observer, viste at det ikke var muligt at fjerne lineariterne i enheden, men det var vist at det er muligt at reducere dem.

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A master thesis from Aalborg University

Compensation of Loudspeaker Driver Nonlinearities Using Predictive and Feedback-Based Approaches