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Show How Coil-Driven Speaker Operates Invention Is Described in British Patent by C. W. Rice. A modification of the Rlce-Kellogjr type of loud speaker Is described In a British patent by C. V. Rice. Renders Rend-ers are no doubt familiar "with this type of speaker, which consists essentially essen-tially of a light dlnphragm driven hy a moving coil working in a strong magnetic field. An electromagnet is utilized, In which the turns are arranged ar-ranged concentrically, the moving coil being located In the annular gap between be-tween the two poles. It is mentioned In the specification that the impedance of the coil at various audiofrequencies Is determined partly by Its ohniic resistance re-sistance and partly by its reactance. j At very low frequencies the Impedance Imped-ance Is due almost entirely to Its resistance, re-sistance, while at higher frequencies the reactive component may predominate. predomi-nate. This, however, tends to give rise to unequal response over the usual speech and music bands, and the object of the Invention is to flatten out the response curve, so that for a given voltage over the entire frequency fre-quency range there will be an equal response. This Is accomplished by associating as-sociating one or two short-circuited turns, preferably in the form of a copper ring, with the moving coil ; so that the copper ring acts as a short- circuited secondary winding to the coll. This, of course, considerably lowers the Impedance of the winding, and hence tends to equalize Its response re-sponse over the entire range, particularly particu-larly with tile higher frequencies. The accompanying illustration Indicates one arrangement of the Invention, where a light diaphragm D, the edge of which is omitted. Is fixed to a coil C wound on a cylindrical form F, nnd joined to the truncated portion of the cone. The magnetic system comprises a cylindrical pole P and an annular pols A, energized In the usu ' way from a source of direct-current supply; sup-ply; and the moving coil C Is located In the gap between the two poles. The coil O is maintained in position partly by means of supports In the form of light rods R fixed to a spider S, screwed to the end of the pole-piece P. The free edges of the conical diaphragm dia-phragm are also supported by thin A Hjj K KM0fnLs w-pL. f XJ A-Jp A new design of coil-drlven loud speaker, which uses copper rings as a short-circuited secondary winding of the moving coil, to reduce the effective ef-fective Impedance at higher frequencies. frequen-cies. lordlier, rubber, silk or similar material. mate-rial. Two copper rings K nre let into the two pole-pieces, I e., the central pole-piece P and the annular built-up pole-piece A. These rings act as a short-circuited, secondary winding to the moving coil C. Lines of force emnnatlng from the moving coil duo to speech currents will, link with the copper rings, thus lowering the impedance im-pedance of the coll, nnd thereby bringing about the desired effect. Wireless World (London). |