Patent ID: 8855356

Claim:
An apparatus comprising: a magnetic assembly including a ring-shaped inner magnet, a ring-shaped outer magnet, a ring-shaped inner cap, a ring-shaped outer cap and a ring-shaped washer, the inner magnet and the outer magnet concentrically mounted on top of the washer with opposite magnetic polarities, the inner cap mounted on top of the inner magnet, the outer cap mounted on top of the outer magnet, the magnetic assembly configured to produce a magnetic field having a zone of operation between the inner cap and the outer cap, the zone of operation having magnetic field lines substantially perpendicular to an ideal motion direction, the zone of operation having substantially uniform magnetic field strength, the zone of operation having a width of 0.90 millimeters and a height of 3.00 millimeters, the inner magnet and the outer magnet each having a width of 2.00 millimeters and a height of 2.00 millimeters, the inner cap and the outer cap each having a width of 2.00 millimeters and a height of 3.80 millimeters, the washer having a width of 5.10 millimeters and a height of 1.00 millimeter; and a voice coil disposed in the zone of operation of the magnetic field and mechanically coupled to a diaphragm of a driver, the voice coil being a four-layer coil with each layer having twenty turns of wire, the voice coil having a maximal width of 0.2032 millimeters and a height of 1.016 millimeters, the voice coil configured to move within the zone of operation of the magnetic field when an alternating current passes through the voice coil, the ideal motion direction axially aligned with a longitudinal axis of the voice coil.