Electro-acoustic transducer

Claim 2

An electro-acoustic transducer comprising a pole piece, a yoke having a magnetic pole portion facing said pole piece while defining an annular magnetic flux gap therebetween a magnet magnetically coupled to said pole piece and said yoke, a voice coil inserted in said magnetic flux gap, said voice coil haviNg a large axial length compared with the thickness of said magnetic pole portion of said yoke, an annular conductive short-circuit ring disposed concentrically around said pole piece between said magnet and said pole piece, and a diaphragm operatively connected to said voice coil, whereby the magnetic coupling between said magnet and said pole piece caused by the large axial length voice coil is cancelled by said short-circuit ring.

Claim 3

An electro-acoustic transducer as claimed in claim 1, in which said short-circuit ring disposed around said pole piece is made by forming a metal plate into a cylindrical shape.

Claim 4

An electro-acoustic transducer as claimed in claim 1, in which said short-circuit ring disposed around said pole piece is made by winding a metal wire into a coil form and connecting the starting and terminating ends of the wire forming the coil convolutions.

Claim 5

An electro-acoustic transducer as claimed in claim 1, wherein said short-circuit ring is of a material selected from the group consisting of aluminium and copper.

Claim 6

An electro-acoustic transducer as claimed in claim 1, wherein said magnet is of a material selected from the group consisting of aluminium-nickel-cobalt alloy and a ferrite.

Claim 7

An electro-acoustic transducer as claimed in claim 1, further comprising means for causing an A.C. magnetic flux to emanate from the voice coil wherein the portion of the A.C. magnetic flux circulating through the magnet and said pole piece is cancelled by said short-circuit ring.

Claim 8

An electro-acoustic transducer comprising: an annular ferrite magnet having an opening formed in a central portion of said annular magnet; a first annular yoke bonded to one surface of said ferrite magnet and having a circular magnetic pole in a central annular opening of said first yoke; a pole piece disposed in the central opening of said magnet and being concentrically surrounded by said magnetic pole of said first yoke defining an annular magnetic flux gap therebetween; a second yoke bonded to an opposite surface of said magnet from said one surface and connected to said pole piece; a voice coil bobbin operatively disposed in said magnetic flux gap between said first yoke and said pole piece; a voice coil wound on said bobbin and having an axial length greater than the thickness of said magnetic pole of said first yoke; an annular short-circuit ring of non-magnetic material disposed concentrically between said pole piece and said magnet and bonded to said first and second yokes; and a diaphragm operatively connected to said voice coil bobbin.

Claim 9

An electro-acoustic transducer comprising: an annular ferrite magnet having an opening formed in a central portion of said annular magnet; a first annular yoke bonded to one surface of said ferrite magnet and having a circular magnetic pole in a central annular opening of said first yoke; a pole piece disposed in the central opening of said magnet and being concentrically surrounded by said magnetic pole of said first yoke defining an annular magnetic flux gap therebetween; a second yoke bonded to an opposite surface of said magnet from said one surface and connected to said pole piece; a voice coil bobbin operatively disposed in said magnetic flux gap between said first yoke and said pole piece; a voice coil wound on said bobbin and having an axial length greater than the thickness of said magnetic pole of said first yoke; an annular short-circuit ring of non-magnetic material disposed concentrically between said pole piece and said magnet and bonded to said first and second yokes; and a diaphragm operatively connected to said voice coil bobbin.

Claim 10

An electro-acoustic transducer as claimed in claim 7, in which said short-circuit ring disposed around said pole piece is made by forming a metal plate into a cylindrical shape.

Claim 11

An electro-acoustic transducer as claimed in claim 7, in which said short-circuit ring disposed around said pole piece is made by winding a metal wire into a coil form and connecting the starting and terminating ends of the wire forming the coil convolutions.