Patent ID: 6847726

Claim:
An improved loudspeaker driver structure, for driving a vibratable diaphragm to produce sound, comprising: first and second similar annular voice coils, located spaced apart end-to-end on a tubular voice coil form as part of a coaxial voice coil assembly that is disposed about a central axis, drivingly coupled to the diaphragm and resiliently constrained to be vibratable only in a longitudinal direction of the axis; a first annular interfacing pair of magnetic pole faces, configured and arranged to form a first annular magnetic gap traversing a predetermined annular portion of the first voice coil; a second annular interfacing pair of magnetic pole faces, configured and arranged to form a second annular magnetic gap traversing a predetermined annular portion of the second voice coil; a permanent magnet having a first magnetic pole defining a first pole piece, and having a second magnetic pole defining a third pole piece; a magnetic yoke having a first end defining a second pole piece and having a second end defining a fourth pole piece, the first and second pole pieces forming the first annular interfacing pair of magnetic pole faces and the third and fourth pole pieces forming the second annular interfacing pair of magnetic pole faces, the magnet completing a flux loop encompassing, in series: (a) the magnet, (b) the first pole piece, (c) the first magnetic gap, traversing the first voice coil, (d) the second pole piece, (e) the yoke, (f) the fourth pole piece, (g) the second magnetic gap, traversing the second voice coil, and (h) the third pole piece; and at least one conductive metal annular shorting ring, disposed coaxially and configured in a tubular form located in coupled relationship with the flux loop and proximate to both the first and second similar annular voice coils and the first and second annular interfacing pair of magnetic pole faces so as to react to current in the first and second annular voice coils in a manner to reduce harmonic distortion in acoustic output of the loudspeaker where the at least one shorting ring extends across one of both the first and third pole pieces or the second and fourth pole pieces so as to constitute a surface layer extending between each pole piece and extending on each pole piece.