MODELLING AN IRONLESS LOUDSPEAKER BY USING THREE-DIMENSIONAL ANALYTICAL APPROACHES

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MODELLING AN IRONLESS LOUDSPEAKER BYUSING THREE-DIMENSIONAL ANALYTICALAPPROACHESR. Ravaud and G. LemarquandLaboratoire d'Acoustique de l'Universite du Maine, UMR CNRS 6613Avenue Olivier Messiaen, 72085 Le Mans, Franceguy.lemarquand@univ-lemans.frAbstract |This paper presents some improved three-dimensionalexpressions of the magnetic ¯eld created by tile permanent magnetsuniformly and radially magnetized for the design of ironlessloudspeaker structures. All the expressions determined have beenreduced to compact forms. We use these expressions for theoptimization of ironless loudspeaker structures in which the radial¯eld must be radially uniform. Indeed, as ring permanent magnetsradially magnetized are rather di±cult to manufacture, these magnetsare replaced by assemblies of tile permanent magnets radiallyand uniformly magnetized. We present an example of ironlessloudspeaker structure that has been optimized with our three-dimensional approaches.1. INTRODUCTIONTile permanent magnets can be used for manufacturing ring permanentmagnets radially magnetized by stacking them together. Such a wayof manufacturing a ring is commonly realized because ring permanentmagnets radially magnetized are di±cult to fabricate. Consequently,this alternative method consists in using tile permanent magnetsuniformly magnetized. However, they do not exhibit the sameproperties as tiles radially magnetized and can lower the quality ofthe radial ¯eld created by the permanent magnet structure.Manyauthorshavestudiedthe¯eldcreatedbyring[1]-[6], cylinder[7]-[9], tile permanent magnets [10]-[12] or by disk conductors [13]-[15]. All these analytical methods have enabled authors to study thesti®ness or the force between permanent magnets for magnetic bearings[16][17] or couplings [18][19]. More generally, optimizations can becarried out with analytical or semi-analytical approaches [20]-[22]. An