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US 4,289,937 AGranted
Speaker with fine grain ferromagnetic material on center pole or ring
AssigneeMitsubishi Denki Kabushiki Kaisha
InventorsHideo Ikeda, Hideshi Tsuchiya, Masaru Okada
Life of this patent
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Abstract
A speaker comprises a voice coil placed in an air gap between a center pole and a plate wherein a specific ferromagnetic material obtained by forming fine crystalline grains is used on at least one of the surfaces of the center pole and the plate which respectively face the voice coil, thereby providing a speaker having low distortion.
Claims6
A speaker comprising a disc yoke, a ring permanent magnet and centerpole on said yoke, a ring plate on said ring permanent magnet, said centerpole and ring plate being placed so as to create an air gap, and a voice coil placed in said air gap;
- wherein said voice coil produces an AC magnetic field when AC signal current passes through the voice coil;
- wherein at least one of the areas of said centerpole and said ring plate which face said voice coil is formed of different material from the remaining portions of said centerpole and said ring plate, said different material being a ferromagnetic material with fine crystalline grains having an average of sixteen (16) or more grains per twenty-five square millimeters of field of view of a microscope at magnification of 100, and having a reduced magnetic domain size;
- wherein the different material produces a substantially linear magnetic minor hysteresis loop for the magnetic circuit of the speaker.
Dependencies are inferred from the claim text.