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1112 HANDBOOK OF PROJECTION FOR
The armature was a piece of soft iron laminated (built up of thin plates) about one inch in length by onetwenty-fourth of an inch in thickness. Its center was pivoted. It was surrounded by a coil. The magnet pole pieces also were laminated. Lamination improves efficiency in operation.
The armature pivot is of the "knife edge" type employed in the construction of fine scales and other precision instruments. It is a type of bearing which reduces "lost motion" to practically nothing at all. The armature is held in place on the pivot by means of a spring, thus providing the stiffness or friction required to prevent unnecessary wabbling, and at the same time eliminating all lost motion.
PRESENT DESIGN.— The present design of Western Electric disc record reproducer is somewhat different from that described. For one thing it is oil damped, which means the entire mechanism of the reproducer is enclosed in a casing filled with oil. This is an excellent method of dampening or smoothing out any tendency to excessive freedom of movement, or "wobble," on the part of the needle.
In the side of the case opposite the magnetic poles, is a thin, steel diaphragm, to which the needle holder is attached. The flexibility of this diaphragm permits the needle sufficient freedom to follow the record groove undulations. It also serves as the armature concerning the action of which we have talked. One of the magnet pole-pieces is in the form of a circle. It extends around the edge of the steel diaphragm. The other magnet pole-piece is double, and is located opposite the center of the diaphragm, its end a few thousandths of an inch removed from the diaphragm. It has a coil wound