International projectionist (Jan-Dec 1940)

INTERNATIONAL PRGJEGTI VOLUME XV AUGUST 1940 PA NUMBER 8 Sound Screens: Structure und Function PROJECTIONISTS are familiar with, or are actually operating, many recently developed units which are necessary essentials in the modern and efficient projection room. Since the advent of sound pictures, many improvements have been made in practically all of the major units that go into the makeup of a complete picture projection and sound reproduction system. Among recent developments in the field of motion picture projection are several new types of arc lamps that produce a better light at less cost for electrical energy and carbons than their predecessors. New types of projectors now coming into general use have as a salient feature dual shutters which transmit more light to the sound screen. Also now being made available are projection lenses which have their individual lens surfaces treated through new scientific processes that greatly reduce the harmful reflections from the several lens surfaces and thereby cause more light to be passed by the lens. And in the sound reproduction field we have seen the sound system with its rotary stabilizer soundhead, high-power amplifiers, and two-way cellular horn loudspeakers accepted as the modern standard. In all cases, however, the final result which a projectionist is able to achieve by the skilled operation of all this fine equipment is largely dependent upon the type, quality and condition of the sound screen. It is By G. F. HOLLY PHOTOPHONE SERVICE DIVISION RCA MANUFACTURING CO., INC. unfortunate that this most important and comparatively low cost item is seldom given the consideration it deserves. Everyone concerned generally seems to assume that because all the other equipment is functioning at peak efficiency the resultant picture and sound quality must be tops. That the sound screen may be offsetting much of their careful work is often overlooked. Let us approach the problem from another viewpoint. While it is very important that the apparatus project light with the desired intensity and color balance onto the sound screen, the way in which these qualities are reflected by the sound screen is equally important. Similarly, one must consider how well the high quality sound emanating from the stage loudspeaker, is transmitted through the sound screen. Since the sound screen is the only link that is really common to both sound and picture projection, it can be a bottleneck that is seriously detrimental to most effective presentation. • Deterioration Factors It is well known that all types of sound screens now in general use undergo a steady deterioration from the day they are made. Unfortunately, entirely too many theatres do not con sider this important fact and passively suffer the consequences. Although many types of screen bases with several kinds of reflecting surfaces are in general use, the basic make-up of the latter, which often is almost as perishable as a freshly picked banana, is much the same. The average sound screen of today uses as a base a woven cloth fabric which has been bleached and flameproofed. Typical processing may be as follows: To secure opaqueness, two coats of aluminum are usually applied and followed by several coats of flameproofing dope. Then several coats of white pigment may be applied and the surface then roughed up by pinpointing to obtain light diffusion and to make subsequent coatings adhere better. One coat of white pigment then may be applied to the back, and about five more coats of zinc white and titanium on the front may complete the finished surface. The completed screen must now be perforated. An accurate and extremely sharp die punch set must be utilized to secure correct diameter perforations with clean cut margins and thus assure the correct initial sound transmission qualities and a minimum of clogging from the accumulations of dust particles. With a new sound screen of this type, some of the chemicals in the multiple coats of surfacing continue a slow process of evaporation and disintegration. Confirmation of this is AUGUST 1940