International projectionist (Jan-Dec 1940)

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instability as well as stabilizing factors, which are not present in straight synchronous motors. The magnitude of these effects can to some extent be controlled by the external circuit arrangements. Selsyn motors are less readily damped than regular synchronous motors, and for this reason arrangements by which the synchronous motors can be interlocked from standstill are of interest. BLACK LIGHT FOR THEATRE AUDITORIUMS H. J. Chanon and F. M. Falge General Electric Co. The demand for near-ultraviolet radiation, commonly called "black light," in the production of fluorescent effects has shown the need for a technical approach to the problem. New technics of measurement as well as design information, data on sources and material are necessary to insure most effective use of these new media. The paper covers design information on the lighting of fluorescent carpet, decorative wall and ceiling murals, and other decorative applications. Information on light-sources, standard filters for absorbing the visible light emitted by the sources, as well as response characteristics of various types of fluorescent materials have been obtained. The effect of extraneous visible light in masking the brightness of the fluorescent material is discussed. One convenient method of measuring the near-ultraviolet energy from mercury light-sources in existing installations is explained. ACOUSTIC DESIGN FEATURES OF STUDIO STAGES, MONITOR ROOMS, AND REVIEW ROOMS D. P. Loye Electrical Research Products, Inc. A survey was made of studio experience, as one step in the determination of the most nearly ideal design characteristics practicable for studio stages, review rooms, and other units. Acoustic measurements were also made of Hollywood studio units of these types. These data were correlated with the information obtained in the survey, and used as a valuable guide in the determination of the optimum characteristics and dimensions recommended for major studio scoring stages, monitor rooms, dubbing rooms, review rooms and studio theatres. These data are described in detail, and recommendations regarding the studio units are given. These recommendations include the optimum reverberation and other acoustic characteristics, and also the most practicable sizes which experience and theoretical considerations indicate to be desirable. Information regarding Hollywood preview theatres is included in an appendix. GROUND-NOISE REDUCTION SYSTEMS E. W. Kellogg RCA Manufacturing Co. The principal purpose of the paper is to formulate a statement of the desired characteristics of a ground-noise-reduction system, in terms of such factors as prompt opening, peak reading, and filtering. In this it is assumed that anticipation is not employed. It is desirable to limit the filtering to a single stage of resistancecapacity filtering (or equivalent). Slow closing helps filtering and peak reading. The better the peak reading properties of How Much Light • • • onto your screen €y from your screen • Check up on how you spend your Illumination Dollar ! PHOTRIX PHOTOMETER enables you to measure easily and accurately • light incident upon the screen • uniformity of light distribution over the screen • reflectivity of the screen • screen brightness as seen from various points in the theater Photocell search unit is connected by cable to permit its being held conveniently to all portions of the screen. Available with various sensitivity ranges up to 0.01 foot-candle per division, some of them suited for permanent installation to be read from the projection room. You cannot afford to be without this modern instrument .... to evaluate the worth of your equipment and to check its deterioration. Your eye is not reliable in estimating light values. Stop guessing .... and you'll save the price of the Photometer in no time by no longer wasting your money on inefficient equipment. MODEL B Ranges: 0-40; 0-200; 0-400 foot-candles Complete data on request PHOTOVOLT CORPORATION 10 East 40th St. New York, N. Y. OCTOBER 1940 27