GB280772A - Hornless loud speaker - Google Patents

Abstract

280,772. Bothe, O. March 8, 1927. Loud-speakers; magnetic instruments; diaphragms.-In a hornless loud-speaker having a diaphragm freely oscillating parallel to itself, the diaphragm g is centred by a thin non- perforated plate c secured at its centre to the diaphragm and rigidly clamped around its edge to the casing b. The diaphragm is preferably formed from a coarse meshed fabric stiffened by a filling material, such as copal varnish. The diaphragm is produced by moistening a comparatively coarse meshed fabric, such as gauze, cambric, spartery, &c., stretching the moistened fabric over a frame corresponding in shape with the desired shape of the diaphragm, and subsequently drying and impregnating it, e.g. with copal varnish. As shown, the diaphragm is actuated by a moving coil d provided at its centre with a cylindrical extension i which passes through the plate c and is cemented in a hollow extension s on the conical stiffening member k at the centre of the diaphragm g. The coil d is located in an annular magnetic air-gap j formed between the cylindrical core e and the front portion of a hollow spherical ring a. The apparent resistance," i.e., the resistance vectorially composed of the ohmic resistance and the purely alternating resistance of the coil, is made, equal to the internal resistance of the amplifying valve so that the anode current of the amplifying valve can be conducted directly through the coil without the interposition of a low frequency transformer between the valve and loud-speaker. The flat rim of the diaphragm g is clamped between a ring r, secured by arms h to the casing b, and a frame l screwed to the ring r and of such a width as to prevent the sound waves from passing round from one side of the diaphragm to the other.