Patent ID: 6768806
Filing Date: 2004-07-27
Classification: H04R

Abstract:
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; first and second annular magnetic pole faces, configured and arranged as an interfacing pair forming a first annular magnetic gap traversing a predetermined annular portion of the first voice coil; third and fourth annular magnetic pole faces, configured and arranged as an interfacing pair forming a second annular magnetic gap traversing a predetermined annular portion of the second voice coil; a permanent magnet having a first magnetic pole directed to the first pole face, and having a second magnetic pole directed to the third pole face; a magnetic yoke having a first end directed to the second pole face and having a second end directed to the fourth pole face thus providing a main magnetic path around a flux loop encompassing, in series: (a) the magnet, (b) the first pole face constituting a first magnet pole piece, (c) the first magnetic gap, traversing the first voice coil, (d) the second pole face constituting a first yoke pole face, (e) the yoke, (f) the fourth pole face constituting a second yoke pole face, (g) the second magnetic gap, traversing the second voice coil, and (h) the third pole face, constituting the second magnet pole piece, completing the flux loop; and at least eight annular shorting rings made from highly conductive metal, disposed coaxially and located in coupled relationship with the flux loop, configured and arranged to act as a short-circuited winding turn that opposes any change in strength of the flux loop and opposes any displacement so that whenever the voice coils are energized with audio frequency current so as to cause the coil form to vibrate the diaphragm, the rings are caused to react in a manner to reduce harmonic distortion in acoustic output of the loudspeaker, where at least two annular shorting rings are disposed in each of the pole faces in opposite regions such that four outermost of the shorting rings are disposed outside the magnetic flux loop as defined by the center line, and four innermost of the shorting rings are disposed within the flux loop as defined by the center line, where at least one annular shorting ring is disposed entirely within the magnetic flux loop as defined by a center line so as to act in a manner to particularly reduce even order harmonic distortion in the acoustic output.