Patent ID: 7103195

Claim:
A speaker unit comprising: an elliptical vibrating diaphragm; a cylindrical voice coil having a circular cross-section and secured at one end thereof on a center of the elliptical vibrating diaphragm; a rectangular frame for movably supporting the vibrating diaphragm and having a through hole in its center; a magnetic circuit formed by a top plate having a rectangular shape and having a through hole in its center, a plate-shaped magnet having a rectangular shape and having a circular through hole in its center, and a back plate having a rectangular shape and having an integrally formed upright pole on its center, wherein each of the top plate, the plate-shaped magnet and the back plate has a width and a length, each width being substantially less than each respective length, thereby permitting installation of the speaker unit in a narrow space, wherein the top plate, the plate-shaped magnet and the back plate each has a width that is equal to or narrower than a width of the rectangular frame in its shorter axis, wherein the top plate, the plate-shaped magnet and the back plate each has a length that is equal to or shorter than a length of the rectangular frame in its longer axis, wherein the rectangular frame is mounted on the top plate and formed with a through hole on its bottom for inserting the voice coil into a magnetic gap formed between the through hole of the top plate and the integrally formed pole of the back plate, wherein the top plate, the plate-shaped magnet and the back plate are all accommodated in a case made of a magnetic material, with the top plate serving as a cap for the case, wherein the rectangular frame presents a rectangular shape when looked at in plan view, wherein the hole formed in the center of the top plate defines a constant and continuous radius, wherein the rectangular frame has a stepped interior surface and an upper lip overhanging beyond the outer perimeters of the top plate, the plate-shaped magnet, and the back plate, wherein the stepped interior surface comprises a first horizontal surface that is substantially parallel to a top surface of the top plate, a second horizontal surface, located further from the top plate than the first horizontal surface, that is substantially parallel to the top surface of the top plate, a third horizontal surface, located further from the top plate than the second horizontal surface, that is substantially parallel to the top surface of the top plate, a first substantially vertical surface coupling the first horizontal surface to the second horizontal surface, and a second substantially vertical surface coupling the second horizontal surface to the third horizontal surface, and wherein the outer perimeter of the top plate extends beyond an outer perimeter of the first horizontal surface and the first substantially vertical surface.