InventorUS Class335/222With relatively movable coil and permanent magnet (e.g., D'Arsonval type) position on the cathode ray tube)Attorney, Agent or FirmInternational Class H01F 7/122 Issued Patent Number:8121337
Abstract textDisclosed is a free air magnetic circuit and speaker in which no pole piece is used. A magnet layer is located between a top plate and a back plate with a gap defined essentially in the center thereof. Into the gap, a wire coil attached to a diaphragm may be inserted. A magnet flux passes between the top and back plates. In some embodiments, the interior edge of each of the metal plates tapers toward the gap, and the magnet layer extends past the peripheral edge of each of the metal plates so as to discourage magnetic flux between the metal layers at the peripheral edge. | 
