GB261231A - Improvements in and relating to electromagnetic acoustic apparatus - Google Patents

Abstract

261,231. British Thomson-Houston Co., Ltd., (Compagnie Truncaise pour l'Exploitation des ProcÚdÚs Thomson-Houston). March 3, 1926. Loud-speakers; magnetic instruments ; diaphragms.-- In an electromagnetic acoustic apparatus such as a telephone receiver of the kind in which the oscillating system comprises two or more elements separated by a fluid or elastic medium and having different natural frequencies, each element is acted upon directly by the electromagnet. In the loud-speaker shown, two diaphragms M. M' of magnetic material are spaced apart by a washer B and clamped against the casing C by the cover D which carries the horn P. The separating clamping washers B, P, R<1> may be chosen so as to facilitate the regulation of the distances between the two diaphragms and of the diaphragms relatively to the electromagnet E. For example, rubber washers R, B and a paper washer R' may be provided and adjustment may be obtained by screwing the cover D more or less on to the casing C. The electromagnet E may also be adjustable. The plates M, M' are of different thickness so as to have different natural frequencies and their distances apart and from the electromagnets is such that the amplitudes of vibration of the plates are equal when the frequency of the supply current is remote from the natural frequencies of the plates. The plates may be of sheet metal or mica carrying a sheet metal disc or cylindrical moulding. The plates may be circular, rectangular, flat, checkered, or corrugated and may be perforated or have a thickness which varies gradually from the centre to the periphery. Specification 125,645 is referred to.