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A MICROPHONE BOOM ELMER C. RICHARDSON* When sound motion pictures were first produced in the Holly- wood studios, the sets were small, and no great difficulties were en- countered in concealing microphones within the set, so that sound could be satisfactorily picked up. As the sets became larger it became necessary to use a plurality of microphones, and to fade from one circuit to another as the actors moved about. This operation of fading from one microphone to another contributed to errors in recording which while excusable a year ago would be highly criticized today. To obviate the use of plural microphones several devices were used. For instance, a microphone was sometimes suspended from the ceiling by means of a cord and moved about with a long pole, an operation quite obviously called "fishing." Some studios had their property departments construct supporting arms or booms which would facilitate the quick placement of microphones. Most of these pieces of equipment were hurriedly made and crudely con- structed and none too satisfactory in their operation. The Metro-Goldwyn-Mayer Studios, after some experimentation with a microphone boom of this type, designed and built a boom of the type illustrated in Fig. 1, which operated quite satisfactorily. This boom consisted of a substantial base supporting a vertical column which in turn supported a lever arm having an adjustable portion which could be extended or retracted at will by operating a cable drum by means of a crank from the floor. The under- balanced portion of the boom and the weight of the microphone was counterbalanced by a fixed counterweight and the boom operated upon its vertical and transverse axes by an operating lever, as shown in the illustration. While there are some sound engineers who object to the use of moving microphones, many of the best technicians are convinced * Mole-Richardson, Inc., Hollywood, California. (Read before the Society at Washington.) 41 42 ELMER C. RICHARDSON [J. S. M. P. E. that the inherent limitations of the microphone can be overcome by silently moving the microphone to maintain it in a proper relation to the sound source, and by properly manipulating the fader. FIG. 1. Microphone boom designed by Metro-Goldwyn-Mayer. FIG. 2. Extension tube carrier, Type M-R 103-103A. As is true with many of our problems, the general principle in- volved in this design is simple; the real problem, however, was to July, 1930] A MICROPHONE BOOM 43 construct this piece of apparatus so it would operate with a degree of silence which would in no wise interfere with sound recording. In the type illustrated, the sliding tube was operated by two leather-faced friction rollers, which were rotated by a cable which was wound over a capstan sheave. The whole apparatus worked quite silently, but there still slight snapping sound as remained a the wires of the cable changed their position on this capstan. To overcome this difficulty, another type of extension tube carrier was designed. (Illustrated in Fig. 2.) In this case, the extension tube rolls in and out of the fixed tube, supported on a leather-faced FIG. 3. Microphone boom, Type M-R 103-103A. rollerhaving an eccentric adjustment for centering purposes, but instead of being moved by friction it is moved by a direct pull from a cable attached to the rear portion of the sliding member and op- erating in the annular space between the stationary and sliding tubes. This cable passes back to a simple sheave supported at the fulcrum point of the fixed tube and down to the operating drum. It is wound around the operating drum several turns and passes around another simple sheave at the fulcrum point, returning through a sheave in the rear of the fixed tube, and is rigidly fastened to the 44 ELMER C. RICHARDSON [J. S. M. P. E. sliding member. This construction gives a positive motion to the sliding tube with a construction which introduced no serious prob- lems of extraneous noise. This type of boom (M-R 103) is illus- trated in Fig. 3. A number ingenious suspensions for the microphones have of been worked out, such as hanging the microphone on rubber suspen- sion loops and mounting upon sponge rubber shock absorbing mecha- nisms. One of the most successful mountings was worked out in the Pathe Studios by suspending the microphone from the center of a rubber diaphragm about six inches in diameter. By means FIG. 4. Microphone boom, Type M-R 103- A (extended). of these various rubber suspensions all "telegraphed" sounds were withheld from the pickup circuit. Since the microphones have certain directional characteristics many of the studios have taken advantage of this and constructed suspensions which allow the microphone to be faced at will by the operator. In this way, for instance, if a conversation is being carried on between two persons, the microphone may be faced from one to the other, giving better recording results than would be the case if the microphone were held in a constant position. July, 1930] A MICROPHONE BOOM 45 Practically every major studio on the West Coast, and some of the studios in New York, have been using these booms with good success. A demand arose for an automatically counter-balanced micro- phone boom which could be operated from the top of a camera booth. To meet this situation, the M-R Type 103-A boom was developed. The same principles of design for moving the tele- scoping portion have been incorporated in this boom as in the Type M-R but the counterpoise is mounted on a carriage which 103, slideson the rear portion of the fixed tube supported by leather- faced rollers and operated by means of a sheave system working on the principle of a double block and fall. The counterpoise moves outward one foot when the sliding tube and microphone are extended three feet. This gives the advantage of always maintaining the boom in a state of balance, and by underslinging the boom from its fulcrum bearing the boom will always return to a horizontal position when it is released. This boom mounted on a tripod which may be elevated (see is Fig. 4), and has a number of advantages which have been well ac- cepted by the studio operating personnel. It does not matter whether or not one objects to the use of the moving microphones (other technicians are probably more familiar with the pros and cons of that subject), the fact remains that micro- phones must be placed. In the Hollywood studios, a picture of any size iscarrying an overhead charge of from ten thousand dollars a day up. Every minute gained in the production time is money saved. If you have ever observed sound operators trying to place microphones by means of rope suspensions, fishing, etc., it is quite obvious that a device such as has here been described has a very defi- nite place in sound motion picture production.
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