Projection engineering (Jan-Dec 1931)

Page 16 PROJECTION ENGINEERING While the ideal method would be to use a silent camera, until such perfection is attained, it is necessary to place the existing cameras in some form of silencing box. This, in the first place, took the form of a camera booth large enough to house one or more cameras and the cameramen. Being extremely cumbersome and heavy, it was in some cases very difficult to place on a set and of necessity soon gave way to handier methods. During this preliminary stage, much thought and work went into the methods of camera maintenance which re ■ suited in their being brought to a higher state of mechanical perfection than had ever before been attempted in the industry. It was also found that the commonly used means of interconnecting the camera and the camera drive motor by a flexible shaft was a great source of noise. This camera drive was a development of talking picture equipment which the weight of the early motors made necessary, as it was not practical to hang much weight on the camera structure. At this period each studio investigated camera silencing in its own way. By a process of experimentation and elimination, the present-day devices were evolved. They are by no means ideal and are being continually changed and improved. The generally accepted opinion is, of course, that the ultimate solution of this problem will depend on the development of a silent camera which it will not be necessary to enclose. In camera booths, the natural development was along the lines adopted by most studios (with a few exceptions), that is, an individual camera enclosing box which, in its early stages, was simply a wooden framework covered with various sound insulating materials. This did not silence the camera sufficiently to permit its use within fifteen or twenty feet of a microphone and it was soon replaced by more efficient designs. It is unnecessary to follow the various stages of this development, but from a survey of the present-day equipment it is easy to see that it is simply an elaboration of this silencing box. The new camera silencing devices became known as "blimps" or "bungalows." In the majority of cases the bungalow was made to contain the drive motor as well as the camera. Some of the studios adopted a form of drive motor which was mounted directly on the camera ; others retained the flexible shaft but enclosed it inside the bungalow. One or two of the studios made separate bungalows for the motor and the camera, and covered the flexible shaft with heavy layers of sound insulating material. The Fox Movietone Studios adopted as standard a camera bag composed of rubberized cloth, kapoc floss, and other soft insulating materials, fastened by means of zippers and snaps. The lens and finder protrude through the bag. With the adoption of the heavy bungalow covered camera, a very much stronger and more rigid camera-tripod became necessary. The bungalows used by Warner Brothers and United Artists are light enough to mount on the standard tripod. Most of the other studios adopted either a tripod which was developed by Metro-Goldwyn-Mayer in collaboration with Pathe, or else an adaptation of this, used in conjunction with a standard tripod for rigidity. The Academy of Motion Picture Arts and Sciences, under date of May 14, 1930, published through their Technical Digest Service, Report No. 3 of the Producers-Technicians Committee relating to camera silencing. This report gives in detail a complete resume of all such devices in use at that time. It includes information on the insulating value in decibels, the methods of construction, materials used, and the distance that a microphone can be used from the camera. Noiseless Recording Methods The noiseless method of recording on film, announced at the end of 1930, appears to be receiving general acceptance throughout the industry. RCA Photophone has described two methods of effecting noiseless recording on variable width track. One of these displaces the zero line on the track in such a manner that the clear portion is only just wide enough to carry the modulation. This is subject to the disadvantage that weaving in the projector may cut off some of the weaker sounds. The second method uses a movable shutter during the recording which causes the clear part of the sound track to become blackened in those portions which are not employed to carry the modulation. The Western Electric Company has announced a noiseless recording system which is applied to their variable density method. The density of the sound track is increased during the intervals in which the sound volume is low, and is decreased according to the envelope of the sound currents in such a manner that the film is always just able to accommodate the required modulation. The Fox organization has devised a means for flashing lamp variable density recording, in which the intensity of the lamp is reduced during the intervals of low sound amplitude, the intensity being altered during the process of recording. A number of independent makers of sound equipment, most of whom are using the flashing lamp, have announced attachments to their equipment which produce essentially similar effects. The reduction of noise is accomplished during the actual recording by an attachment to the recording system, and, in general, involves no change in recording or processing technic. The amount of noise reduction which is being employed in most studios at ' the present time is of the order of 10 db. Set and Studio Acoustics — Theatre Acoustics Extensive investigations have been made by many interested in the factors concerned in set and studio acoustics and theatre acoustics. In some cases these studies have been made with recently developed instruments, permitting more accurate results than those previously obtained by aural methods. Several factors have been discovered by such means, some of which have contributed to the development of a more general formula for the computation of the time of reverberation. The application of this formula, which has been published by Dr. C. F. Eyring, of the Bell Telephone Laboratories, is of particular value in set and studio work, where average absorption coefficients are comparatively high. Important studies of the effect of relative humidity on sound absorption are being made. The necessity for consideration of the reverberation existing throughout the frequency spectrum is now well appreciated. Whereas many enclosures had in the past been acoustically treated, giving consideration only to the reverberation at 512 cycles, experience -in many of these cases indicates the necessity for obtaining suitable balance between the reverberation at the low and high ends of the frequency spectrum relative to that in the central portions of the range. It is becoming the practice to adjust theatres and recording studios to have times of reverberation throughout the frequency spectrum such as will give definite rates of decay for sounds of equal loudness. With the application of suitable accurate instruments for the measurement of reverberation times, studies have been made of the relative effects of connected volumes, which have an important bearing on complex auditoriums, as well as on recording sets on large stages. Further study, by instrumental means, has indicated the effect of direct reflection to be of importance and requiring consideration in the design of auditoriums, in addition to the consideration given the reverberation time. The importance of maintaining a very low noise level has been extended to cover not only the studio, but the theatre. This has become more necessary with the development of recordingmethods insuring a lower background level in the sound picture. Attention must be given to the transmission of