Uppsala universitet

Linear Quadratic Gaussian Controllers for Feedforward Active Noise Control

Pushing performance and moving towards adaptive control.

Annea Barkefors

Licentiate Thesis, Signals and Systems, Uppsala University, May 2014.

The thesis summary in Pdf

Paper copies of the complete thesis can be obtained from Ylva Johansson, Signals and Systems Group, Uppsala University, Box 534, SE-75121 Uppsala, Sweden.

Active noise control is a research area focused on using destructive interference of sound fields to attenuate undesired noise. Methods for active noise control are best suited for low frequency noise, as the complexity of the problem grows rapidly with frequency. Coincidentally, passive means of damping have the opposite quality in that they work better for higher frequencies and become bulky and impractical for low frequencies.

Applications for active noise control range from fan noise in ducts, noise-cancelling headphones and noise in cars to propeller induced aircraft cabin noise.

In this comprehensive summary, the underlying principles of active noise control are presented and the control problem is discussed. Several aspects of the control system are introduced to give an introduction to the research papers that are the basis of this licentiate thesis.

The work behind the thesis is focused on a Multiple-Input Multiple-Output (MIMO) Minimal Mean Square Error (MMSE) Linear Quadratic Gaussian (LQG) feedforward controller. This controller is shown to achieve uniform damping in an extended region in space and push the upper frequency that can be controlled. The influence of different design variables has been investigated, and the properties of the control path analyzed with consideration of its ability to suppress noise of prescribed spectral properties over an extended region. In this context, it has been shown how to use the reproducibility of the primary noise path by the control path as an indication of achievable performance for a given control system.

Finally, the controller has been adapted to follow changes in the primary noise statistics, an approach that seems promising to considerably raise the performance of the controller.

Publications included in the Thesis:
IEEE ICASSP 2012: Extending the area silenced by active noise control using multiple loudspeakers. In Pdf

IEEE ACC 2012: MIMO design of active noise controllers for car interiors: Extending the silenced region at higher frequencies. In Pdf

ICSV19, 2012: An investigation of a theoretical tool for predicting the performance of an active noise control system. In Pdf

Paper in IEEE TASLP 2014, Design and analysis of Linear Quadratic Gaussian feedforward controllers for active noise control. In Pdf

Paper at InterNoise 2014 on adaptive control in nonstationary noise settings.

Related work:

AES 48th Conf. 2012: Acoustical zone reproduction for car interiors using a MIMO framework.

PhD Thesis by Simon Widmark 2018 on causal MMSE filters for personal audio.

PhD Thesis by Lars-Johan Brännmak 2011 on robust sound field control for audio reproduction.

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