Supervision: Hervé Lissek
Project type:
Semester project (master)
Master thesis
Assigned
The spherical sound source is known to be an optimal geometry, due to the limited scattering effects over the sphere when compared to other geometries (circular or rectangular planar pistons for instance). However, this shape is impossible to realize with conventionnal loudspeakers, apart from some approximations (the dodecahedron sources, used for room acoustics measurements, among others).
The Corona Discharge (CD) principle has been demonstrated to allow achieving linear acoustic flow velocity source without relying on an intermediate membrane, presenting an almost perfect electroacoustic transduction with an extremely sharp impulse response. The CD loudpeaker generally consists of two electrodes, a "corona" electrode of extremely thin size (array of wires, needles, etc.) put at a sufficiently high voltage to ionize the surrounding medium particles, and a "collector" electrode, conductor of larger size than the "corona" connected to the ground, attracting the ions while being sufficiently transparent to particle streams (eg. a metallic grid).
With this configuration, the CD loudspeaker presents a combination of two intrinsic sources: a monopolar "Heat" source, due to the local heat exchanges occurring in the ionization process, and a dipolar "Force" source, resulting from the electrostatic force accelerating the charged particles (and the surrounding medium) back and forth around the transducer. This transducer has been proven to be an ideal flow velocity source, and a recent PhD thesis proposed a detailed model of the transducer that can serve now for further optimization.
Besides the absence of membrane, this arrangement allows imagining various geometries that are not possible with membrane-based loudspeakers. Especially, it could be the ideal transducer to achieve the so-called "pulsating sphere", an ideal source that is generally used as a model for omnidirectional sources, but that cannot be realized with conventional types of loudspeakers.
The proposed semester project intends to work on identifying and eventually implementing a purely omindirectional CD loudspeaker configuration, and if time allows, extrapolate towards other types of canonical electroacoustic sources (cylidrincal, linear antenna, circular antenna, etc.).
The project will consist in the development of a COMSOL (and/or analytical) model of the transducer(s), that will serve for geometry optimization. After defining a set of optimal geometries, one or several prototype(s) will be constructed and tested in anechoic conditions.
Content
- COMSOL and/or Matlab simulations
- Electroacoustic measurements
Prerequisite
- BA5-Electroacoustique
- or MA1-Audio Engineering