The Ring Armature Telephone Receiver

' HE ring armature receiver is a new type of telephone receiver developed for use in the subscriber's telephone set. It differs from other types in that the diaphragm consists of a thin, lightweight, domeshaped central portion made of low density, non-magnetic material whose function is to radiate sound energy, surrounded by a narrow ring-shaped armature to which it is attached. The ring armature is not clamped at the outer periphery, but is held in place solely by magnetic attraction. It is driven at its inner periphery by the magnetic force. A ring-shaped pole and magnet structure serves as the motor element to drive the diaphragm. The new receiver is shown in sectional view in Fig. 1. The advantage of the composite diaphragm construction in the new receiver is that the central portion moves almost wholly like a piston and is therefore nearly 100% effective and that its contribution to the total moving mass is small, being of the order of For these reasons it has been found possible to reduce the mass per unit area to approximately ^ of that of the diaphragm of the bipolar receiver. Because of the large effective diaphragm area and the low mass, the acoustic impedance of the new receiver is low, being about 7 of that of the earlier receiver. Although the motor efficiency is approximately equal to that of the bipolar receiver, the improved diaphragm construction yields a receiver of higher available power response, 1 wider frequency range, improved characteristic when the receiver is held off the ear, and having greater discrimination against room noise.