GB209761A - Improvements in or relating to electrodynamic telephonic transmitter or receiver - Google Patents

Abstract

209,761. Siemens & Halske Akt.-Ges. Jan. 12, 1923, [Convention date]. Magnetic instruments; loud-speakers.-In an electrodynamic telephone receiver or transmitter in which the diaphragm itself forms the conductor through which the line currents pass, the diaphragm, consisting of a strip of metal foil, is given a preliminary resiliency in a longitudinal direction, either by corrugating it transversely and stretching it when fixed, or by a spring mounting, or both. The mass of the diaphragm is preferably made equal to the mass of air which it causes to vibrate. The diaphragm a, Fig. 3, preferably a strip of aluminium foil, is mounted between an insulating part b and a conducting part c and clamped by a screw d. It may be stretched over spring blades x, Fig. 5, which are adjustable by screws y. The part of the diaphragm which is clamped may be coated electrolytically with copper; the coating being thicker within the terminal clamp. A filling of lacquer or other substance, which will be resilient when dry may be run into the angles between the diaphragm and the clamps. Two or more diaphragms may be used in series or parallel or series-parallel, and the wires leading to them are arranged in loops as in Fig. 4 so that, when an electromagnet is used, the induced currents in the loop due to variations in the supply current are neutralized. The diaphragm is exposed to the air on one side only, there being a closed adjustable chamber, preferably lined with felt on the other side. The Specification as open to inspection under Sect. 91 (3) (a) also states that, to ensure a uniform action on the diaphragm to neutralize the skin effect, the magnetic field is arranged so that its action is stronger in the middle than at the edge. This subject-matter does not appear in the Specification as accepted.