International projectionist (Jan-Dec 1936)

Servicing Theatre Sound Picture Reproducing Equipment By C. C. AIKEN RCA MANUFACTURING COMPANY ONCE a sound motion picture reproducing equipment is installed in a theatre, the following problems are faced : (1) Maintaining high quality. (2) Avoiding faulty operation and failures. (3) Adjusting to changing recordings. (4) Adjusting to new standards. (5) Modernizing when feasible. (6) Gaining experience leading to advancement. The maintenance of high-quality reproduction depends largely upon the same factors that are involved in design: (a) The beam from the exciter lamp must be uniform, steady in intensity, of the proper size, and vibrationless. (b) The movement of the film must be free from variation in linear speed, weaving, or fluttering. (c) The electrical system must be free from extraneous noise or distortion, and must have sufficient amplification and a proper frequency response characteristic. (d) The conversion from electrical impulses to sound waves must be without extraneous noise or distortion. (e) The sound waves must be directed so as to provide uniform results throughout the auditorium, without allowing the room itself to introduce objectionable factors. The standards of performance and the methods of measuring items (a) to (d) are determined in the laboratory in connection with the design. By extremely close contact between the field and the laboratory groups, the initial standards and methods and the subsequent changes are made known and put into operation in the field. Criteria of Quality The final criterion of quality is the human ear; but as between various persons, the response of the ear varies enormously. Audiometer tests show a variation of as much as 40 db. among individuals. For a given person, the ear responds differently from hour to hour. To avoid having such variation Vital factors in a well-rounded servicing program for theatre sound reproducing systems are contained in this article, first presented before the S.M.P.E. Projectionists generally, and particularly those already engaged in servicing work, will find much of interest and value therein. introduce inconsistencies, the standards set up in the laboratory, in so far as possible, are expressed in terms of objective measurements rather than subjective sensations. In many cases, the objective laboratory methods have been found to be directly applicable to field use, providing accurate, stable standards for the maintenance of high-quality reproduction. In cases when the ear must be relied upon without the aid of objective measurements, it is necessary to devise special tests by means of which defects in reproduction are caused to be accentuated so that the trained ear can readily detect them regardless of the listener's state of fatigue. In this respect it is important that the field engineer develop an acute sense of hearing by long and continuous training. He must have an excellent standard of comparison and must have had long experience listening to reproduction under many conditions if he is to be able to diagnose equipment accurately to determine whether it is in the best of condition or not. Experience Determines Procedure The field practice to be followed in correcting faulty functioning and failures is determined by experience. The proper procedure is the one that works best by actual test. Systematic accumulation of experience of a large field force in thousands of theatres forms the best possible basis upon which to lay the foundations for these procedures. In the same way that the design of equipment undergoes change from year to year as new and better methods are [12] developed, field procedures go through an ever improving evolution. Closely allied with the application of field experience to field practice is the application of field experience to engineering and research. Theory and practice are prone to diverge unless theory is constantly checked against actual results. The sound motion picture art can not develop at the speed it should unless it takes full advantage of its experience. By watching the leaders of the industry, smaller companies are prevented from diverging too far from the path of sound progress, but for the good of the motion picture business as a whole the larger companies may not neglect to follow the products of their development. The recordings of some producers are lacking in the bass; others over-em rhasize the bass notes, and in some the high-frequency response is so garbled as to make it necessary to equalize the highs. As a rule, a satisfactory compromise best suited for the product being shown at the time can be found. But for best performance, changes in the reproducer characteristics are required to be made when the majority of features shown in a theatre are obtained from a different producer or when a change is made in the recording characteristics. Fads introduced in the march toward perfect reproduction carry us too far, first in one direction and then in another. At one time popular opinion required crisp speech of optimal intelligibility; and, at another time, booming, rearing, lowfrequency response was demanded. As a matter of good business policy it is necessary to adjust the theatre equipment in accordance with the prevailing tastes, and to change them as the tastes vary. In spite of, or, perhaps because of, the vicissitudes of show business, progress has been rapid. New tastes, new developments, new requirements have made obsolete in a few years the early theatre equipment (and should have made obsolete much of the recording equipment), demanding either the purchase of new and modern equipment or