The motion picture projectionist (Nov 1931-Jan 1933)

22 Motion Picture Projectionist November, 1931 waves to travel through a consequently restricted area, he was permitted to load the diaphragm, obtaining greater response from the air and consequently a greater amount of energy was transmitted into it. Also, the loading of the diaphragm contributed to its operation as a whole and prevented undesirable cross vibrations. Speaking of his device Tigerstedt says, "In devices of the type referred to it was common practice to provide, opposite the diaphragm, a guide for the sound waves, as, for instance, a mouth-piece or the like, having a central opening for the passage of the sound waves. "Since the central opening in the guide was usually comparatively small, the mass of the diaphragm caused to vibrate by the sound waves was also comparatively small. Thus, with devices, as heretofore constructed, much difficulty has been experienced in transmitting sound waves to somewhat far distances, and no mechanism has, to my knowledge, heretofore been devised embodying any practicable means for enabling a clean transmission of sound waves to far distances so that they will be clearly comprehended at distance places. "The object of the present invention is to obviate the aforesaid difficulties and to correct a vital imperfection. To this end I provide means wherebythe sound waves will be conveyed from the rim of the diaphragm to its center and vice versa, thereby enabling the diaphragm to be acted upon by or to produce a greater quantity of sound waves." Gruber's Work In 1929, Gruber took advantage of this principle and invented a speaker, the driving mechanism of which was placed within the heart shaped plug near the surface of the plug consisting of a small cone. Gruber describes his device as follows: "In connection with talking machines, loud speakers, broadcasting receivers and the like, it is common practice to use a diaphragm of small size, say from one and one-eighth inches to two inches in diameter, in connection with a horn having a maximum cross diameter much greater than that of the diaphragm. Of recent years there has been a tendency to substitute, for the horn and small diaphragm, a hornless apparatus, consisting as far as practicable of a diaphragm of relatively large size. "This offers advantages of simplicity, compactness and lightness, together with possibilities of cheapness. In order to give adequate volume to the sound produced, however, it is necessary to employ some expedient to cause the entire diaphragm, or a large portion of it, to move as a unit in the production of sound waves. As a rule, it is desirable to make either the diaphragm stiff, or to maintain it under tension, or to brace it at a plurality of points in order to insure that the diaphragm, when actuated, will as far as practicable execute piston-like movements against the air. Certain Difficulties "A conical diaphragm, either stiff or under tension is appropriate for the purpose just mentioned, but here arises a difficulty. If the conical diaphragm be too small, it does not make contact with a sufficiently large area of the adjacent air, and if too large, it does not readily execute the required piston-like vibratory movements, and especially for the finer overtones. It is indeed a difficult matter so to proportion a particular diaphragm as to give it an area large enough for adequate volume, and yet small enough for fidelity in the reproduction of the higher overtones, and of complex and delicate sounds. The usual expedient is a compromise, namely, the use of a conical diaphragm not less than nine inches and not more than fifteen inches in diameter. "I have made the discovery that by the use of a relatively small diaphragm of suitable form, say a conical diaphragm four, five or six inches in diameter and operated under tension or not as conditions may reciuire, coupled with a reflecting sound chamber of special form and used as hereinafter described, I can give proper expression to a wide range of overtones, and produce sounds of great delicacy and complexity, and yet can produce adeouate volume such as is not ordinarily produced except by a diaphragm of much larger size or by the addition of a horn." Graff also used a flat diaphragm attached to a unit located within the plug and used an adjustable surface adjacent to the bottom of the plug by means of which he adjusted the distance between the diaphragm and the case to create a resonance period suitable to the ear of the operator. Hensley studied refinements of air chambers from 1915 to 1923 and employed plugs of various shapes, sizes, materials and consistency. The Amplion Octophase A recent unit of interest is the Amplion Octophase. This unit employs the movable coil motor contributed by Sir Oliver Lodge, the principle of the piston diaphragm taught by Edison, Stroh, Coombs, and others and takes advantage of the principles of tone chamber construction taught by Eickemeyer, Tainter and Tigerstedt. In addition, refinements have been added whereby the area over the dome shaped diaphragm is divided into eieht divisions. The centers of gravity of eafh of these divisions are exactly equi-distanl from the throat of the unit. Channels are provid°d wifhin the tone ch^^ber to gather the sound impulse* from ea^h division and reach the throat of the horn in perfectly timed synchronism with the arrival of sound impulses from all the other divisions. The application of the design principles above enumerated, permit the construction of a unit capable of reproduction of sound frequencies over a wide range with comparatively uniform efficiency. The use of horns of heavy wall material with highly polished interiors correctly designed, results in a highly directional speaker. In such a device, the sound energy provided by the power amplifier is directed in -i beam effect to the areas desired, not only avoiding the waste of energy, but sound waves are prevented from striking reflecting surfaces, such as ceilings and side walls, thus eliminating objectionable echoes and greatly reducing the period of audibility of a sound of any given intensity. This directional or beam effect also causes the sound to reach the listener from the direction of the speaker rather than from the various reflecting side surfaces, thus avoiding distraction of attention and creating a pleasing illusion, particularly in motion picture work. Kliegl Issues New Catalog Kliegl Brothers of New York, manufacturers of lighting specialties, have announced the publication of a completely revised new catalogue, with list prices adjusted to presentday levels, and with the very latest improvements and new devices for theatrical, decorative, and spectacular lighting, such as footlights, borderlights, spotlights, floodlights, and numerous other forms of lighting equipment and apparatus included in its pages. The publication is complete in every respect, fully illustrated, thoroughly indexed, and conveniently arranged for quick reference. The new Kliegl Catalog A is available to anyone interested in lighting. Copies may be obtained, free of charge, by a request addressed to Kliegl Bros., 321 West 50th street, New York, N. Y. Kaplan Society Holds Dinner Dance The annual dinner dance of the Kaplan Projection Society, the educational and scientific division of Local 306, Moving Picture Machine Operators Union was held in the Grand Ballroom of the Hotel Commodore on Saturday night, October 31st. A gigantic entertainment was provided which was staged under the direction of Larry Kent, chief of the short subject division of the Paramount-Publix Long Island City Studio, and Arnold Van Leer of the R. K. 0. organization.