International photographer (Jan-Dec 1934)

January, 1934 T li e INTERNATIONAL PHOTOGRAPH KK Eleven felt; so there is very little reverberation within either room. This monitor theatre is provided for the sole purpose of simulating normal theatre sound conditions as closely as possible ; and its construction and acoustic treatment are such that time of reverberation within it is practically the same as that of a small motion picture theatre filled with an audience of average size. This arrangement per instead of the two panels that are standard for the permanent equipment ; but otherwise there is little difference between the two installations. The monitor man must of course wear headphones when using the portable monitor desk, because it is usually placed in position on the set beside the camera where the monitor man has a good view of the action. This type of monitoring equipment would supersede all other types because of its convenience, were Center — The monitor desk in operation on a set. Courtesy Universal Pictures Corp. Right — The portable monitor desk, showing the amplifier and junction box for microphone cables beneath the opened door. Courtesy Universal Pictures Corp. Left — A portable monitor booth. The junction box for microphone cables is clearly shown. The small horn of the monitor man's public address system may be seen on top of the booth. Courtesy Paramount Productions, Inc. mits the monitor man to hear the sound he is monitoring under conditions similar to those which will exist when an audience listens to the recorded sound being reproduced in a theatre. In this way, the monitor man works under acoustic conditions that are as nearly normal as it is possible to make them. The Portable Monitor Booth Where there are so many sets left standing on the stage that their intervening walls obscures the monitor man's view of the set in which shooting is being done, a portable type of stage monitor room, or monitor booth, is often used. This monitor booth is a small, thoroughly sound-proofed room about five feet square and seven feet high mounted on regular automobile wheels ; and resembles closely the old-style camera booth. It is just large enough to hold the monitor man, his monitoring contro's, and a small horn. A large, double-thickness window with an air space between the sheets of glass is provided in the front of the monitor booth to allow the monitor man a clear view of the action on the set ; and access to the booth is through a closely-fitting door of double-wall construction in the rear. Insulated and shielded cables equipped with suitab'e plugs are used to connect the monitor booth with the main recording system. The monitoring equipment in the booth is essentially the same as that in the permanent monitor room. Batteries to supply current for the monitoring amplifier are carried in the booth. The monitor booth is preferred by some monitor men because it can be moved right up beside the cameras on the set to the position most advantageous for observing the action ; and when so used it permits much more intimate monitoring work. The Portable Monitor Dask A new type of portable monitor desk is now becoming popular with monitor men. This is a desk with a slanting front something like the permanent control desk ; but it is mounted, together with a chair and. a box for batteries, on a platform equipped with large casters. Only a single three-position mixing panel is used in the portable desk, Please mention The International Photographer when corresponding with advertisers. it not for the unsatisfactory reproduction that the headphones provide on anything other than straight voice recording. The arrangement of the microphone and system cables will be apparent from the accompanying photograph. Monitor Horns and Units The two monitor horns installed in the permanent monitor room are of the exponential, air-column type, and have lengths of twelve and fourteen feet, which assures good reproduction of the bass notes in recording music. The greater the length of the air column, which is measured from the diaphragm of the horn unit to the opening of the bell, the lower the frequency response of the horn. That is, the fourteen-foot horn will reproduce lower musical notes than will the twelve-foot horn. The horn units are of the electro-dynamic type, which has a high factor of efficiency in converting energy from electrical to sound form. These units operate on the same principle that accounts for the functioning of the dynamic speakers used in radio receiving sets. The theory involved will be explained in another chapter. Field current is supplied to the units through series resistors from a twelvevolt source. These horns and units are of the same type as those employed in motion picture theatres. The monitor horn installed in the portable monitor booth is of the same type as those used in the permanent monitor room, but it is smaller, which results in a loss of response to the low-frequency end of the sound spectrum. This small horn is equipped with the same type of horn unit that is employed on the large monitor horns. The horn is mounted on the back of the monitor booth in a box-like affair built onto the outside of the booth beside the door. This arrangement is provided so that the opening of the horn wall be at the greatest possible distance from the monitor man's ears. Because of the poor lowfrequency characteristic of the small horn, the monitor booth is never used when music is monitored. For the recording of dialogue and sound effects, however, the lack in low-frequency response of the small horn is not objectionable.