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1945 Theatre Catalog, 4th Edition, Page 345 (321)

1945 Theatre Catalog, 4th Edition
1945 Theatre Catalog
1945 Theatre Catalog, 4th Edition, Page 345
Page 345

1945 Theatre Catalog, 4th Edition, Page 345

and M-11 Dual, two electro-dynamic high frequency units and a double horn throat are furnished to accommodate the paralleled output of the two power amplifiers in these models. This also gives a highly desirable emergency feature.)

The high frequency horn furnished with this speaker system has 32 cells. This multi-cellular horn is of superior type in respect to the requirements for ediciency and for the widest and most uniform distribution of sound energy. Physically, this horn incorporates entirely new design and construction practice. It consists of an assembly of individual primary cells bolted together at their open ends and securely held in a die cast common throat at the other ends. Each primary cell is then divided into four compartments. The primary cells are non-resonant zinc a110y die castings insuring strong physical properties and a light but rigid aSSembly.

The two 15-inch electro-dynamic low frequency speakers furnished in the loudspeaker assembly are newly designed and offer excellent performance ability and efficiency. The use of two speakers gives an excellent emergency feature in addition to providing better bass respouse. The low frequenCy folded horn employed in this loudspeaker system contributes heavily to the high efliciency, wide coverage and overall excellent performance of the complete loudspeaker system. Provision is made in the folded horn to accommodate the two 15-inch low frequency speaker units and the crossover filter network.

The crossover filter network is provided with an adjustable high frequency channel attenuator so that the level of output may be varied to suit the particular needs of the installation. The crossover frequency of this network is 400 cycles per second.


Good sound reproduction must be achieved if present-day critical audiences are to be satisfied with moving picture theatre programs, and good sound reproduction will result only when each of its contributing factors is designed so that it will play its part most efficiently in helping to create sound of pleasing fidelity. From the sound track on the film to the acoustics of the auditorium, each element must not only perform its own function without intros ducing appreciable distortion or noise, but it must pass the signal to the next unit in the chain ef'liciently and with full regard for the characteristics of the next unit.

One of the major advancements toward high-fidelity sound is the RCA r0tary stabilizer type of :oundhead. That it has overcome noticeable fiutter, or pitch variation, has been proved not alone in the laboratory but in its wide use in theatres. A sustained note, like one from a piano, is reproduced as it originally sounds, and spoken words are heard clearly and di:tinctly.

Yet the rotary stabilizer is only one of several features of sound-head construction which combine to make possible better sound reproduction.

The mounting of the exciter lamp,



optical system, photocell, and scanning drum as a separate, shock-insulated unit inside the main soundhead case prevents these important parts from receiving and transmitting normal soundhead vibration. Hence, film passes smoothly through the light beam. Furthermore, the exciter lamp filament and the photocell elements, being free from jar, do not introduce microphonic noises into the sound.

A factor of importance is the method of driving the picture projector; if it is driven from the sound sprocket shaft, any vibration or variation in projector speed and load will tend to cause comparable vibrations, or changes in speed, in the sound sprocket.

A refinement found only in the RCA deluxe soundheads is that of shockproof drive. This mechanical device is so constructed that irregularities of drive of both the picture projector and the lower take-up mechanism are carefully excluded from the constant speed sprocket shaft of the soundhead by driving these

from the soundhead hold-back sprocket shaft. Any variations are thus filtered out mechanically without reaching the independent constant speed shaft. This refinement results in higher quality more uniform sound, particularly when lower takeoups and picture projectors become faulty and irregular through continued use.

If the film is pulled through the light beam directly by the sound sprocket (as it is in some soundheads), those vibrations or speed changes are transmitted to the film, and immediately cause characteristic distortion. The seriousness of this condition is eliminated in the rotary stabilizer soundhead, because the film speed is controlled mainly by the stabilizer, with a loose film loop between it and the sound sprocket.

The use of ball-bearings on all soundhead shafts insures good, steady operation for a long period of time, there being negligible wear to affect the normally smooth operation of the soundhead. All soundhead drive gears operate in an oil


1945 Theatre Catalog, 4th Edition, Page 345