International projectionist (Oct 1931-Sept 1933)

May 1933 INTERNATIONAL PROJECTIONIST 15 minor modifications were needed to make them entirely suitable. New Amplifier Development This was not true of the amplifiers. There had to be developed amplifiers which would faithfully transmit all ^ frequencies from 35 to 16,000 cycles at levels from the barely audible pianissimo effects to the resounding orchestral crashes of ten million times greater power; and all the pieces of apparatus had to be so designed that even during intervals of complete silence not the slightest noise would be introduLed to suggest the presence of electrical apparatus. No underlying hum or noise, such as is commonly present in radio or other systems of reproduction, could be tolerated with the new apparatus. In the intervals of silence there must be real silence; a dead auditory void in which the fall of the lightest pin could be heard. This has actually been accomplished to a degree heretofore unknown. Probably the most quiet electrical reproduction up to the present is that obtained with high-grade sound picture apparatus; but such apparatus at ■a its most quiet moments gives off 300 times more sound than the new apparatus when the musicians are silent. Of even greater difficulty possibly was the design of suitable loud speakers. It is not practicable to obtain the entire frequency range with a single unit, and so two types of loud speakers are used. One, somewhat resembling the horns used for sound pictures, is employed for the frequencies from 35 to 300 cycles; and another type, for the range from 300 to 16,000 cycles. These loud speakers are different from anything previously produced commercially. Never before have these elements fulfilled such difficult requirements of frequency range and volume. The best sound picture system record and reproduce approximately half the range of frequencies handled by the new loud speakers, and the best radio systems even less. In volume range the comparison is equally remarkable. Although sound picture systems under the most favorable conditions may provide a volume range of 40 to 45 db, radio systems rarely exceed 30, while the range provided by the new apparatus is well above 80. Whereas the power range of radio is of the order of 1,000 to 1, the new equipment is capable of yielding a range of 100,000,000 to 1. Improved Sound Distribution The new loud speakers and their associated equipment of amplifiers and microphones are, therefore, fully capable of handling the entire volume range of a symphony orchestra. When one speaks of range of loudness which can be handled by an electrical system for reproduction, one is concerned with the differences between the loudest and faintest passages of the music which it can reproduce. There is in addition the problem of handling the peaks of maximum loudness. These peaks in the case of music from a symphony orchestra are beyond the possibilities of the ordinary loud speaker to reproduce without distortions which seriously affect the musical sonority. The low frequency sounds make the largest contribution to the peaks of sound power which must be handled to meet these conditions. The diaphragm of the low frequency element in the new loud speaker has been made nearly seven times larger than that of the Some question may arise in the minds of our readers as to the quality superiority of Auditory Perspective transmission over that customarily experienced from the operation of standard sound motion picture equipment, such as is used in theatres. In this connection, aside from the fact that the former embraces especially developed amplifiers and loudspeakers together with associated apparatus, having an effective overall response characteristic of about 30 to 16,000 cycles, there will be remembered the comparison involves direct pick-up and transmission to the auditors of the sound on the one hand, while on the other we have an indirect or delayed transmission wherein the sound after being picked up is stored in a record (film or disc) , later to be taken off and transmitted. More losses are naturally introduced under the latter conditions, the sound passing as it does through several energy transformations. Further, it will, of course, be appreciated that the Washington Auditory Perspective demonstration represents the consummation of a certain amount of research work and was presented as an experiment, and therefore was not subject to economic or physical limitations such as surround the commercial exploitation of sound equipment for any given purpose. — Editor. elements used ordinarily for sound picture reproduction. By these diaphragms a large column of air is set into motion. The ordinary loud speaker also becomes directional in its characteristics at the higher frequencies. Low frequency sounds spread in all directions from the mouth of the horn, but the higher frequencies tend to concentrate into a beam projected directly ahead of the horn; and the width of the beam becomes narrower and narrower as the frequency increases. Because of this fact, the audience, in a large hall equipped with the ordinary loud speakers, never hear quite the proper blending of frequencies. Those directly in front of the horn receive too great a proportion of the higher frequencies, while those on the sides receive too much of the low frequencies. To avoid this effect, the horn of each highfrequency element is divided into 16 diverging rectangular sections which spread the sound over an arc of 60 degrees vertically and one of 60 degrees horizontally. Two of these units placed side by side thus spread the sound over a horizontal angle of 120 degrees — a far wider coverage than has been obtained before and one which distributes the sound thi'oughout the auditorium with a faithful blending of the frequencies. Besides providing for the full volume range of the orchestra, the amplifiers have an additional amplification of at least 10 db, so that, if desired, the volume of loud passages may be made ten times as great as the actual output of the orchestra. Technically described, the maximum sound power of a symphony orchestra integrated over an interval of two-tenths of a second is less than 20 watts, whereas that possible from the loud speakers of the new apparatus is more than 200 watts. This additional gain allows effects to be obtained which have been impossible before. Besides the effects of range and quality of tone, the total aesthetic appeal of an orchestra is due in no small degree to the range in volume. The number of musicians one can place on a stage is limited. To put ten times as many as contained in a modern symphony orchestra is impossible in any existing hall. The control of volume given by the new apparatus enables the director to secure at will the equivalent of an orchestra of nearly a thousand musicians. The advantage of this control of volume does not end here, however. Its presence makes it possible to reproduce operatic music, where a soloist is accompanied by an orchestra, without allowing the voice of the singer to be drowned out by the louder passages. For this purpose a third channel, including its separate microphone, transmission line, and loud speaker, has been provided in the new system (Continued on next page)