Motion Picture Herald (July-Aug 1935)

84 MOTION PICTURE HERALD July 2 0, 19 3 5 TECHN€L€eiCAL The BLUEBOOK School By F. H. RICHARDSON BLUEBOOK SCHOOL QUESTION NO. 274 (one of a special group on sound).— (A) When should a photocell be replaced? (B) Why Is it Important not to disturb the position of the exciter lamp optical system after the focus has been correctly set by the manufacturer's representative? (C) What general precautions should be observed when replacing tubes In an amplifier? Answer to Question No. 268 Bluebook School Question No. 268 tvas: (A) Explain why a flywheel is used in most sound reproducer sets. (B) As a projectionist, what do yo-u regard cls the most fertile field for improvement in sound syston design, particularly with the object in view of greater convenience in operation of the equipment? Answering Section A, the engineers who subniited this question say, "One of the requirements of faithful sound reproduction is that the film shall move past the scanning beam (sound head aperture) at an absolutely steady, unvarying rate of speed. Any irregularity or jerkiness of film speed past the sound gate aperture will show up in the form of flutter (What about "wows?" — F. H. R.) which is ruinous, particularly to music. The sound or constant speed sprocket that moves the film past the aperture is driven by the same motor as both the take-up and the projector mechanism. It therefore follows that any uneven load, as for example in the take-up or the intermittent movement, or any intermittent or uneven binding in any of the many gears or shafts in the mechanism may be reflected back to the sound drive and cause uneven motion. In order to minimize this effect, a flywheel is attached to one end of the sound sprocket shaft. When the balanced and relatively large mass of the flywheel is in motion, it tends to prevent any small, sudden changes of speed in the sprocket, thus insuring steadiness of speed." As to Section B, there were several answers, the practicability of which I would not presume to pass judgment upon. Many suggestions were evidently impracticable; a few just plain impossible. Evans and Rau say, "The most fertile field for improvement in sound system design would be (referring to equipment, not service) some method of securing a fine adjustment of the exciter lamp optical system that would hold it at the right point while locking it into place. The later, up-to-date equipments are as convenient as could be desired, so far as has to do with "operation. We are unable to suggest any needed improvement." A. Sprafke says, "I have a few, perhaps fantastic, ideas, though I do believe they will one day become realities. First, that the present system of amplification, due to extensive development of design and tube development, be re duced to a small panel that would require little space, thus reducing the time and trouble when checking in case of emergency. This would tend to reduce the hold-up of the show when trouble comes. My second idea is to eliminate the present necessity for constant manipulation of the fader by so recording the sound intensities, and so marking them that the projectionist, knowing the particular sound level of his theatre, would be able, at the start of a show, to set his fader where it should be and let it stay there. By this I mean that aside from differences in response of various auditoriums, the sound intensities should be taken care of entirely by the studios in the recording." In part, I believe this is not at all a fantastic idea. However, the projectionist would nevertheless still have to manipulate a fader. Brother Sprafke has overlooked the fact that many things more or less constantly alter the auditorium response. For e.xample, the theatre is half empty at one time, and filled at another, and we all well know that calls for a volume change. Even light summer clothing and heavy winter wear makes a lot of difference, as do many other items. B. DeVietti says, "One idea for improvement in sound system design has to do with sound and picture changeover — the synchronization of the two. It seems to me this could be accomplished by connecting the picture changeover mechanism with the fader in such manner that zero fader would occur as the changeover is made. When the fader is moved past zero on F.H.RiCHARDSON'SNEW BLUE BOOK OF PROJECTION A new edition of this famous book is now on the press. Projection, sound reproduction and trouble-shooting all in one compact, handy volume of 700 pages, including 153 illustrations of hook-ups, wiring diagrams and schematics. Experts ecBsidar it th« m*st up-t*-date and practical proje«ti»R maaual en the market. Centains an extremely simple index tystem for Instant use in emergency breakdewns. A kwk that sheuld be part ef every projection reen in the country. Order early and get an original author's eutegraphed copy. QUIGLEY BOOKSHOP 1790 Broadway either side, the dowsers would operate automatically, and the changeover of both picture and sound occur simultaneously. "Another thing: Why not have some sort of an apron attached to the lower magazine door that would keep the film from dropping on the floor when the door ij open and one is threading? It might be some sort of a flexible apron that would fill the space between the magazine bottom and open door. That the end of the film does get on the floor and thus accumulate dust is indisputable. Possibly what I have said is not what is wanted by the engineers, but I do believe either or both would help to some extent." D. Danielson says, "Further extension of the frequency reproduction range, either by improved emulsions and optical design, or by speeding up the film movement (projection speed) should, in my opinion, have first consideration. Second, the design of new systems to provide a large reserve of undistorted power, and the renovation of present systems to meet this requirement. Only thus may proper volume illusions be created. Perhaps this may not come, for in the future lies development of fourth dimensional sound or auditory perspective, using not less than three accurately calibrated recording and reproduction channels." H. Edwards says, "The chief convenience to the projectionist would, it seems to me, be a complete instruction booklet, containing not only wiring diagrams so made that the average projectionist can understand them and trace them out, but also instructions so compiled that their exact meaning is clear. All engineers seem to have the idea that because something is perfectly clear and exceedingly simple to them, it should be to all others, which is far from being true. Those compiling instruction books should take the position that those reading them do not know anything about the subject being dealt in — which is too often the exact fact." And now here is one that I believe deserves very serious consideration by sound engineers. It is by Charles Oldham, Norwich, Conn. "Designers of sound systems should base their reasoning upon reports of the most frequent sources of trouble reported, making such modifications as ivill tend to stop or at least reduce those troubles. All equipments should be tagged or marked as to where voltmeters or head phones may be attached for testing work. All switches and fuse blocks pertaining to the sound system installed in the projection room should be in an approved type of panel, which is not always now the case. The amplifier rack and indicating lights should be constantly under the observation of the projectionist when at his post of duty beside the projector."