ELECTRODYNAMIC TRANSDUCER AND USE THEREOF IN LOUDSPEAKERS AND GEOPHONES

摘要

The invention relates to an electrodynamic transducer including a frame and containing at least one electric coil (2) which is placed in a static magnetic field and which can move about a rest position in a vertical free space. The aforementioned coil(s) is wound around and fixed to a mandrel (12) and a return means is used to return the coil-bearing mandrel to the rest position in the absence of an external bias, said straight cylinder defining an inner volume and an outer volume. According to the invention, the magnetic field is produced by outer and inner magnetic structures which each comprise at least one fixed permanent magnet in the form of a ring. The motor does not contain any ferromagnetic or magnetic part between the outer volume and the inner volume. Moreover, at least the part of the frame that is used to fix the magnets is made form a non-ferromagnetic and non-magnetic material. The ratio R of the inductance value L_p of the coil when at rest and blocked in the transducer to the inductance value L_l of the same coil when free and isolated in the space is between 0.9 and 1.1 in the useful frequency band of the transducer. Numerous implementation variants are disclosed in the invention.