Projection engineering (Sept 1929-Nov 1930)

Projection Engineering, April, 1930 Page 17 In the preliminary paragraphs of this article the statement was made that one photocell did not suffer from frequency restriction. This is true only of the vacuum cell, the effects in the gas-filled type are shown in Fig. 10. This curve was taken with a rotating wheel light interrupter in con 90 80 70 60 50 f "IG .■10 \ f It 30 20 << & VAC ;uui> A CI :ll 10 10 20 30 40 50 LIGHT INPUT FREQUENCY K.C. 100 °/o MODULATED Frequency sensitivity of photoelectric cells. nection with a variable speed motor. At low frequencies an oscillating neon tube may be employed. The photoelectric cell is an extremely high impedance device up to the point where the inter-electrode capacitance becomes a factor in shunt. In conjunction with a suitably designed amplifier it is operative from any desired low frequency up to a high frequency limit determined by the stray admittances of the amplifier circuit. Regardless of output considerations (the cell has the highest output when working into an impedance comparable with its own), the circuit impedances must be kept low however, as to avoid any cut-off at the high frequencies due to the stray capacities assuming a value effective in shunt with the true circuit elements. In sound work it is usual to employ an amplifier in close conjunction with the cell, working into a low impedance line. The photocell amplifier is adjusted to bring the level in the line up to that of the magnetic pickup employed with disc recordings. 15 (0 Id a. 10 LI 0 nP V *o> &> 2 SO^ .1 .2 .3 .4 .5 LUMENS FIG. K\ Light-flux-anode current of gasfilled photocell. Thus it is only necessary in changing from disc to film pickup to throw the necessary switches, without regard to changes in level other than applicable at the fader. Bibliography Metcalf— Proc. I.R.E. Vol. 17, No. 11. Hull— G. E. Review, Vol. 32, No. 7. Roller— J.O.S.A. Vol. 32, No. 7, Vol. 19, No. 3. MOSS PROPOSES CHAIN OF THEATRES FOR TALKING PICTURES BS. MOSS announced his return to the amusement business recently, after a retirement of two years, with the disclosure of plans for a series of theatres which will be "acoustically perfect and scientifically designed for the talking pictures." These new theatres, Mr. Moss said, will be revolutionary in construction, will be the first in the world to be scientifically designed to provide the best acoustical reception possible for talking pictures and "will immeasurably enhance the enjoyment of theatre patrons." Between forty and fifty such houses are projected for New York and various other parts of the country. Anticipating the early development of the full stage, or big screen picture and possibly, of television motion pictures, the theatres will be so constructed that they may be readily adapted to either or both mediums, Mr. Moss said. The first theatre of the projected chain will be a $2,000,000 structure at Eighth Avenue and Twenty-third Street, to seat 2,500. Mr. Moss said he had already obtained title to a site 200 by 200 feet. Demolition of the present buildings is already in progress and construction will be begun at once, so that the theatre may be opened in about six months. Radical innovations, said Mr. Moss, both in physical structure and in materials, have been adopted to bring about improved acoustical reception. The auditorium will be shaped like a large bell, cut in half, the seats will be arranged something after the pattern of an open fan, so than all will be in line with the sound waves. "Talking pictures" said Mr. Moss, "cannot be successfully presented in houses where hard walls and balconies, protruding ornamentation and hard floors and seats combine to hurl back a reverberating and distracting discord of sound repercussions to harass audiences seeking relaxation and entertainment. The 'talkies' must have their own houses, completely sound-proofed and constructed in accordance with the fundamental acoustical principles with which modern science is now thoroughly acquainted. The old 'shooting gallery' type of picture house — four bare walls, a screen and a bird's nest projection booth — can no longer serve." The walls, ceilings and floors will be lined with a dampening material known as acoustical tile, so that the sound waves are snuffed out the instant they reach the confines of the auditorium, instead of being echoed back. Another feature of the equipment will be a remote control whereby the sound reception will be regulated in the rear of the auditorium by an acoustical engineer, who will hear the tones exactly as the audience hears them and wTho can immediately correct or modulate any sound effect by the manipulation of his control devices. This feature, Mr. Moss said, was inspired by similar apparatus used in broadcasting studios, which makes it possible to hear a program exactly as it is being broadcast. "All these tests," said Mr. Moss, "have convinced me that the voice can be reproduced perfectly with every nuance of expression and every modulation of tone, in properly designed theatres. This is why, after two years of retirement, I am impelled at the age of fifty to return to the theatrical business." PORTABLE SOUND EQUIPMENT WITH Governor Trumbull, of Connecticut, as guest of honor at the first demonstration of its kind ever held in the State, the first program of entertainment presented through the medium of RCA Photophone portable sound reproducing equipment, played to a capacity audience in the miniature theatre installed as the feature attraction at the annual Pageant of Progress in the State Armory, Hartford. Following the projection of a number of short subjects, Governor Trumbull made a close inspection of the portable equipment and publicly commented upon the remarkable advance in the science of sound photography. "This is most interesting," he said, "and particularly to me because I have given considerable study to the art of motion pictures. I believe the sound picture ultimately will play an important part in the education of our boys and girls and that it also will be employed by many industries." An amusing situation arose while Governor Trumbull was in the midst of his opening address on a stage adjacent to the theatre. The operator of the portable projection apparatus accidently turned the switch controlling the sound and with most abrupt suddenness and with ususually loud volume, the voice of a character in a sound picture punctured the atmosphere. Governor Trumbull glanced toward the little theatre at about the time the operator shut off the sound and remarked : "I see I have some competition."