International projectionist (Jan-Dec 1940)

a line with progressive delay, and two lines with progressive delay and a pressure gradient element. GENERAL AND DESIGN CONSIDERATIONS OF LOW-NOISE MICROPHONES A. L. Williams and H. G. Baerwald The Brush Development Co. With the development of the microphone art toward increased fidelity, thermal agitation noise becomes the principal limitation and therefore a major problem. Its physical side has been discussed in a recent publication where the factors on which noise performance depends have been analyzed, and a suitable noise rating based on aural perception has been proposed. The purpose of this paper is to outline some practical consequences. Different microphone types are discussed in regard to their noise performance and. particularly, to their inherent limitations of noise reduction. Multiple piezoelectricmicrophones which lend themselves particularly well to the design of quiet units, are treated in more detail. The noise performance of different sound-cell types is given including a recent developmental unit which tends to realize the inherent efficiency of the piezoelectric type of microphone to a fuller extent. The practical realization of the qualities of piezoelectric units in a microphone depends on a suitable choice of the associated circuits and tubes; the principles and limitations of their design are indicated. Application is also made to the design of minimum-noise combinations of different microphone types, particularly to an adjustable hypercardioid (unidirectional) combination of ribbon and soundcell type. Some performance data of a corresponding experimental model are given. SOME FACTORS INFLUENCING VOLUME RANGE IN PHOTOGRAPHIC SOUND RECORDING W. K. Grimwood and O. Sandvik Eastman Kodak Co. This is an extension of an earlier investigation of background noise. The present paper deals more specifically with the relation between volume range and the type of photographic materials and the sensitometric conditions used. A brief study of the effect of the spectral quality of the radiation used in recording and printing is included. MEASUREMENT OF PHOTOGRAPHIC PRINTING DENSITY J. G. Frayne Electrical Research Products, Inc. When the spectral sensitivity of positive film is simulated by the use of a suitable combination of phototube and optical filter in the integrating sphere densitometer, the printing density of any type of negative, irrespective of grain size, with any tvne of base or backing, may be accurately determined. Printing density is practically independent of the type of light source or filtering employed in the printer. Relationships between printing and visual diffuse densities for various types of negatives have been established. G.E. SOUND-LEVEL METER A new portable sound level meter, lighter and more compact than any previous instrument of this kind, has been de That's the case of many of your patrons. To secure desired screen brilliancy with today's dense black-and-white pictures and proper projection of colored films, a snow-white light is required .... twice as much light as is possible to project by any low intensity lamp. The Neiv 19000 Series Intermediate Capacity Direct Current Projection Arc Lamp delivers this light at a cost of only 2c an hour more than the lowintensity. It has been designed for theatres of up to 800 seats and using screens as large as 18 feet in width. There are more Simplex High Lamps installed in smaller theatres than any other make. Distributed by NATIONAL THEATRE SUPPLY COMPANY — There's a Branch Near You. PRECISION ALL METAL REFLECTORS dktn'6utec/6i/ NATIONAL THEATRE SUPPLY CO. EXPORT JE.RPBININC. NEW YORK CITY MANUFACTURED BY HETBR-SKUITa INC. OCTOBER 1940 29