The motion picture projectionist (Oct 1928-Oct 1929)

12 The Motion Picture Projectionist September, 1929 (Continued from page 10) merits and are the only portion of the sound head that will need occasional adjustment, a clear fielt1 of light being maintained in the photo electric cell window at all times. The photo electric cell is located at the top of the sound head and the small voltage changes as received from this cell are passed into the film amplifier located on the front wall of the projection room. This amplifier is used to raise the electrical volume to the same level as that of the disc reproducer prior to its entrance into the main amplifier. The batteries for the film amplifier are located directly in under the film amplifier for both simplicity and the saving of expensive conduit runs and wiring. They are located in a box 6" x 24" x 12" and are mounted directly in front of the projector out of the way, yet are at all times readily accessible. Photo Electric Cell Amplifier The film amplifier is mounted directly above the film battery box and is an integral part of this assembly. It consists of a two-stage transformer coupled amplifier of the highest type, uses standard tubes, and the filaments of the tubes are lit from the exciter lamp battery used in the film attachment. A battery box is supplied for the 12-volt storage battery required, and the only switch to be thrown is the one supplying 110 volt, A. C. power to the charger. This does away with expensive charging panels and costly conduit runs and wiring. The Fader The fader (Fig. 5), is essentially a constant impedance potentiometer and is inserted between tne outputs of the film amplifiers, magnetic pickups for disc, and the main amplifier. It is so arranged that various volumes may be obtained and either machine may be "faded" into. There is a key mounted on the fader that switches from film to disc equipment and vice versa. 10YAI ' ||| 1 . HMHi 1 1 1 mm I i^^^ sums! "/• ^ fet Wm ^^fc, ' ■ \\\ V i <r nil Hi ■B : * * : ■H Fig. 4. — Sound film compartment on Royal Amplitone installations. The li I in passes through the chamber horizontally. Wiring There are two pairs of fourteen wires leading from the booth to back stage for the speakers. One pair supplies the 110 volt, A. C. or D. C. power for the excitingwindings of the speakers and the other pair carries the voice frequency currents. Contrary to the usual practice of splitting the speaker supply at the booth, Royal engineers are taking the speech back stage in one pair of wires and are then splittingit up by means of an auto transformer to match the impedance of the speakers. This saves considerable in the line of conduit runs and wire and allows for much better impedance matching, than other systems which are not taking into account the differences caused in low impedance circuits due to the varying length of runs in various houses. Projector Unchanged The projector essentially remains the same. Contrary to the usual belief that constant speed cannot be obtained with the normal Simplex belt and friction disc drive. Royal engineers set about to prove that it could be done and succeeded. A smooth-running projector with belts and clutches in good condition will operate equally satisfactorily as compared with expensive motor and direct drive equipment. This is an additional saving passed on to the exhibitor. Power fluctuations are taken care of where necessary by means of synchronous motors. Royal engineers carefully inspect each projector and make such recommendations as may be necessary for the successful operation of the equipment. Loud Speakers Dynamic cone type speakers are used, mounted on 4 foot baffle boards. They are located directly behind the screen, giving perfect illusion. These speakers each have incorporated within them a miniature rectifying system to supply direct current for their exciting windings. This further does away with the use of batteries and their continuous upkeep care. Any of the perforated or loosely woven fabric screens now on the market may be used. Fig. 5. Royal fader 5,500 U. S. Theatres Wired for Sound Pictures Latest reports indicate that there are more than 5,500 theatres in the United States wired for sound pictures. Western Electric, which seems well on the way to making good its promise to wire 3,000 theatres in 1929, leads in installations with a monthly average of more than 250 installations. A majority of the early installations were for disc reproduction only, but sound on film attachments are now in great demand. Western Electric will probably top its estimate of 3,000 installations this year, according to word from its subsidiary, Electrical Research Products; Inc., who are daily adding new installation shifts to its roster. RCA, which is pushing its new P2 sound projector, is also making rapid progress and seems assured of even more busi ness when its new SpoorBerggren wide film process is marketed. Demand Film Attachment De Forest Phonofilm is quite strong in the West and South, and appears to be making new gains in the East. Royal Amplitone reports the best business month of its history, an advance which is attributed to the recent announcement of the Royal sound on film attachment. The lack of a suitable sound on film attachment has spelled finish for many of the so-called independents, theatre owners being unwilling to take a disc installation alone and then have to shop around for sound on film facilities. Since producers supply pictures with sound on disc as well as on film, many theatres having only disc equipments are content to run along for a while without a sound film attachment.