Motion Picture News (Oct-Dec 1930)

60 Motion Picture News December 6 , 19 3 0 New Metal for Arc Problems By M. H. GOLDBERG Golde Mfg. Co., Chicago With the passage of silents and the solid reflecting surface of the opaque screen discarded, the perforated sound screen has come with a period of brighter light source to counteract the loss of light both at the source (photography) and at the screen (reproduction). High intensity and high intensity reflector arcs of many makes provide this brighter light source with a few attendant practical problems which have been solved in the laboratory in theory. In actual practice, however, we find these problems continuously cropping up and not as smooth-working as preliminary lab tests would have you believe. Here we are, rotating a carbon, feeding it forward, horizontally during rotation, delivering current to that carbon (all while the carbon is being heated so that it might perform its work) to produce light. Excessively high heat intensity is required— a temperature which will melt every metal known — at the crater of the arc. Luckily we have carbon clamping, rotation and feeding an inch or so back of its hottest point and this small difference in temperature allows the use of several metals. However, the metal to be used must resist the intense heat, the seevral gases formed by oxidation of the carbon, must be a good current conductor and must be mechanically sound for holding alignment. Very few metals will serve the purpose of all of these requirements. While one may withstand the attack of the gases formed, and be a good current conductor under ideal conditions, the intense heat will eventually break it down. Metals now in use are suitable for the job under ideal conditions but not wholly under usual rigid operating conditions. Although we find that brass, nickel and allied alloys may be good current conductors and withstand the attacks of gases, they do neither unless the surface within the contacting area of the carbon is entirely free of other matter and bright with only the metal of which it is formed. To keep the carbon jaw in this condition requires constant polishing and cleaning of the contact surface. Unles sthe jaw is cleaned once in at least ten hours running time, harmful effects become apparent. Poor contact between carbon and jaw soon beegts "arcing" between these two points. This arcing is of high enough temperature to melt and breakdown the surface of the metal. The New Sexton Volume SECOND in the series of "American Theatres of Today" was this week issued by Architectural Book Publishing Co. Edited by R. W. Sexton, it contains nine sections, including: Tendencies in the Design of the Present-day Theatre, by Sexton; Design of the Modern Theatre, by Armand D. Carroll; Standard Method of Planning a Theatre, by Albert Douglas Hill; Decoration of a Theatre, by Harold W. Rambusch; Electrical Installation in the Modern Theatre, by Edward B. Silverman; Theatre of Tomorrow, by Ben Schlanger; Theatre Acoustics, by Edwin E. Newcomb; Heating and Ventilating a Theatre, by Edwin A. Kingsley; Theatre Owner and the Architect, by Leon Fleisch whole jaw soon overheats, the carbon is "frozen" in the jaw, it cannot rotate or feed forward and the jaw is ruined unless miled down to clean contact surface. Even with constant daily polishing, the impossibility of maintaining a perfect contact at all points of the contact surface is evident. If a point instead of surface contact is obtained, overheating and melting soon occur. Some metals will not break down under intense heat, but an oxide formed on the surface soon increases the resistance to passage of the current. The constant cleaning will in too short a time reduce the jaw below its proper size, so that center distances are changed with an attending change of relation with the negative carbon. 'it is clearly evident then that the most of replacement very quickly mounts into quite a sum, aside from the trouble caused — poor light, breakdown of light, fluttering due to non-rotation, mottled field of light, etc. In order to cut the cost of replacements, inserts of other rare metals able to withstand all these conditions are tried. Here, however, another situation develops: Oxidation between metal surfaces soon cause the same condition as oxidation between carbon and metal. The breakdown which follows ruins both the jaw and insert. This has been proven in actual practice. However, a solution to these carbon problems appears in a metal composition never before used for carbon jaws. It will not burn out or corrode, does not necessitate constant cleaning and will not hold back the rotation of the carbon and proper feeding, delivering the full cur Theatre Noise Must Be Reduced (Continued from page 51) ness of speech for good articulation. Before the advent of our present type of improved sound recording on film, audience and other noises in the theatre as high as thirty-five decibels were not objectionable as the surface noise of the film was of the same order of magnitude. In the future it will be necessary to reduce the average noise of the theatre if the exhibitor and the audience are to derive the benefit of improved recording. Although under normal conditions we are seldom aware of a noise level of forty decibels above threshold, as soon as intelligible speech sounds are introduced, its magnitude becomes more apparent. We must increase our sound source energy to a sufficient degree to overcome this conglomeration of noise. This in turn leads to distortion and unnaturalness, for it is a fact that the required intensity of sound reproduction should be commensurate with the energy level at which they were originally recorded. Should this not be the case the result is most annoying and displeasing. A recorded whisper may be uniformly amplified within the limits of the equipment, but the result is not a shout, which would normally be expected under noisy conditions, but is an unnaturally loud whisper. This incongruity tends to destroy necessary illusion. There is one more detrimental effect that outside noise may have although the sound being reproduced in the theatre be of sufficient volume and articulation to be naturally understood. We refer to the distracting effect of sudden noises, such as the blowing of automobile horns. Should this sound penetrate the theatre it will prove subconsciously annoying. This creates a dissatisfaction which the patron, more often than not, will lay to the program rather than to its real cause. Fortunately this will be overcome when proper precautions are taken to exclude noises. There is no reason why detrimental noise levels should be tolerated in the theatre as it is a relatively easy matter to measure the magnitude of such noises and to make proper recommendations for their isolation or reduction. rent transferred to it from the source of supply. Although the process of manufacturing this metal is held highly secretive by two American and one German company, its use as contact surface in carbon jaws has been awarded Golde in return for the latter's reesarch for its development.