GB388069A - Improvements in electrodynamic devices for use in receiving or transmitting sound - Google Patents

Abstract

388,069. Sound transmitting and receiving devices. ELECTRICAL RESEARCH PRODUCTS, Inc., 195, Broadway, New York, U.S.A.-(Assignees of Thuras, A. L.; 243, Waverly Place, New York, U.S.A.) Aug. 18, 1931, No. 23288. Convention date, May 2. Addition to 333,578, [Class 40 (iv), Telephones &c]. [Class 40 (iv.] An electrodynamic transmitter or receiver of the kind described in the parent Specification is provided with two additional acoustic impedance devices for controlling the movements of the diaphragm, one of these being an auxiliary air damping device such as is described in Specification 382,668, for damping the vibrations of the diaphragm over a narrow band of frequencies in the upper part of the audible range, and the other additional impedance device comprising a conduit which connects the air in the casing of the instrument with the external atmosphere. This third impedance element, which in itself forms the subject-matter of Specification 382,268, serves to increase the movements of the diaphragm in the lower portion of the audible range. The transmitter shown is substantially identical with that shown in Fig. 8 of Specification 382,668, with the exception that the additional feature provided in accordance with this invention consists of a tube 61 which is secured at one end to the annular polepiece 14 and extends into the chamber 53 formed by the casing 52 in which the magnet structure is housed. A plate 33 and washers 31, 32, between which the diaphragm 27 is clamped, are provided with openings 64 leading to the tube 61. The tube is thus open to sound waves impinging on the front of the diaphragm, and conducts a portion of the sound, particularly the lower frequencies, to the . rear of the diaphragm, thereby producing a reinforcing effect. The conduit 61 may extend through the side of the casing 52, instead of communicating with the external air at a place near the periphery of the diaphragm. A diagragm showing an electrical analogue of the mechanical and acoustical vibratory elements of the device is given in the Specification, together with a graph showing the improvement in the response produced by the invention.