Tristan LEBRUN' Thesis

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with the jury :

Philippe Herzog, Report, ARTEAC-LAB
Françoise Lamnabhi-Lagarrigue, Report, CentraleSupélec
Hervé Lissek, Examiner, École Polytechnique Fédérale de Lausanne
Claude-Henri Lamarque, Examiner, Ecole nationale des travaux publics de l'Etat
Benoit Fabre, Examiner, Sorbonne Université
Bernhard Maschke, Examiner, Université de Lyon
Antoine Falaize, Examiner, La Rochelle Université
Thomas Hélie, Thesis Director, Ircam

"Passive multi-physical modeling, identification, simulation, correction and control of loudspeakers on target behaviors"

Abstract :

This thesis concerns electrodynamic loudspeaker modeling, simulation and control.

Regarding modeling, we adopt a component-based approach that relies on port-Hamiltonian systems. Several linear and nonlinear phenomena are thus modeled and then aggregated in a multi-physical framework. Particular attention is paid to the impact of thermal effects on electrical and mechanical components, for which we introduce new irreversible conservative models. The simulations regenerate known complex behaviors.
A first open-loop control is developed to eliminate distortions by differential flatness. In order to provide the controller with the model's nonlinearity parameters, an ad hoc estimation method is proposed. This combines a separation of the measurement into sub-signals (organized in a homogeneous order of non-linearity) and the optimization of a cost function (improving the contrast between orders). After numerical validation, estimation and control methods are applied on a test bench. The estimated physical parameters are consistent but the re-simulated time signals indicate the need of improvement of the model at very low frequency and to use higher homogeneous orders. The real-time corrector leads to a measurable reduction of the distortions on the sound pressure. In addition, another open-loop control is developed to compensate for the Doppler effect due to the movement of the membrane.
Finally, methods on closed-loop control are proposed. One targets acoustic absorption by combining "control law in finite time" (for efficiency) and "passivity" (for robustness). The other, more general, develops an "half-physical, half-digital" method of connection between a physical system and a digital controller that makes the passivity insensitive to the delay introduced by the digital signal processor.

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