Magnetic device for use in acoustic apparatus

Claim 1

A magnetic device, comprising: means forming a magnetic circuit and defining a magnetic gap between two opposed surfaces thereof, said magnetic circuit forming means including a magnet, a center pole secured to an upper surface of said magnet, and a yoke enclosing said magnet and said center pole such that said magnetic gap is formed between said yoke and said center pole; acoustic vibration producing means disposed in said gap; at least one uni-directional metallic member composed of silicon steel, having low iron loss and permitting movement of magnetic lines of force generated by said magnetic circuit substantially in only one direction, mounted on at least one of said two opposed surfaces adjacent said magnetic gap, wherein the magnetic field generated by said magnetic circuits is confined substantially to that field which passes directly between said opposed surfaces defining said magnetic gap and wherein said at least one metallic member is disposed on the top surface of said center pole adjacent said gap; further metallic members disposed on opposed surfaces of said yoke adjacent said gap; and a still further metallic member disposed on a side surface of said center pole adjacent to and outside said gap.