Patent ID: 7929726

Claim:
A planar diaphragm acoustic loudspeaker comprising: a housing, an acoustic waveguide, a planar diaphragm having a planar electrically conductive coil, and a high flux density magnetic bias circuit; and said planar diaphragm and said magnetic bias circuit positioned between said housing and said acoustic waveguide and said planar diaphragm capable of acoustically feeding through a feed port of said acoustic waveguide; and said planar diaphragm having a bottom side, a top side nearest said acoustic waveguide, and an acoustically active portion having an inside diameter and an outside diameter; and said magnetic bias circuit first comprising a high flux density residual magnetic field magnetic disk having a diameter smaller than the outside diameter and larger than the inside diameter of said acoustically active portion and positioned near said bottom side of said diaphragm; and said magnetic bias circuit also comprising a T-yoke having a central protrusion nearest said diaphragm and said T-yoke substantially of a ferromagnetic material having a saturation flux density greater than a magnetic flux density induced by said magnetic bias circuit; and said high flux density magnetic disk positioned between said protrusion and said diaphragm; and said magnetic bias circuit further comprising a primary biasing magnet ring having a residual magnetic field and having an inside diameter and an outside diameter and positioned substantially onto said T-yoke with at least a portion of said protrusion within said inside diameter; and said magnetic disk having a first magnetic pole nearest said diaphragm which is substantially opposite a second magnetic pole of said primary biasing magnet ring nearest said diaphragm; and said magnetic bias circuit formed through said magnetic disk, said T-yoke, and said primary biasing magnet ring and a high flux density fringing field between said magnetic disk and said primary biasing magnet ring; and said fringing field at least partially positioned onto said acoustically active portion of said diaphragm whereby an alternating current in said planar coil moves said diaphragm due to said fringing field and emanates acoustic energy through said feed port of said waveguide.