Supervision: Thach Pham Vu

Project type: Semester project (master) Master thesis

Available

Room modes can significantly impair the quality of sound diffusion, in particular at low-frequencies and in small auditoria. These low-frequency resonances are the most difficult to control as passive sound absorbers are unable to damp them efficiently. Fortunately, a new concept of Electroacoustic Absorber (EA) has been developed at LTS2 that allows the effective damping of such room resonances, thus providing a solution for equalizing the sound pressure field within the whole space. Their performance can already be assessed in terms of local room frequency responses (RFR), leading to the identification of the resonance frequencies and resonances quality factor, thus allowing retrieving the decay times of each modes. However, the in-situ measurement of the performance of such low-frequency absorbers are difficult to measure space-wise. Indeed, with the state-of-the-techniques, it would require a rather fine grid of microphones regularly spaced along the room. This quickly becomes impractical, especially with non-rectangular rooms, or as the room dimensions increase. New methods for measuring accurately the sound pressure distribution in the room are therefore needed.

In this project we propose to assess a new signal processing approach based on "Compressive Sensing" (CS) to the problem of room acoustics at low-frequencies. A recent work has led to the development of a mathematical framework allowing the retrieval of sound pressure fields at all positions in the room, from the actual measurement at a limited number of positions, based on a sparse representation of modal sound pressure fields in the room at low frequencies. The method still needs to be validated with numerical and in-situ experimental assessments.

This project aims at applying the developed CS processing to the characterization of modal sound fields, with a view to assessing the in-situ performance of low-frequency EA inside a room. Finally, the measurements are expected to guide the design of the EA, with a view to optimizing their performance in terms of modal equalization within the room.

The project will be structured as follows:

• bibliographic study on compressive sensing for room modal characterization;
• development of a numerical model on COMSOL for understanding and optimizing the measurement;
• development of an experimental validation of the measurement technique;
• assessment of room with a set of EA, and in-situ characterization of the absorbers performance;
• Master project only: investigation on the means to optimize the EA based on the measured performance.

Prerequisite: Electroacoustics / Audio Engineering lectures; Signal processing

Context: Theory (30%), Numerical Simulation (30%), Experimental work (40%)