Radio and Television Today (Jan-Dec 1940)

is the assurance that the equipment will all be properly coordinated, avoiding headaches on the job. With the thought that this particular installation may hold some other points of practical and technical interest for sound men, some of its details are shown in the accompanying illustrations. TECHNICAL PROBLEMS The "Railroads on Parade" show is staged in a great outdoor theatre with a stage that measures approximately 200 feet in length by 125 feet deep. In front of this is a narrow lawn and from this lawn rises a single-deck grandstand with seating accommodations for close to 5,000 spectators. The sound problem is complicated by several things. Absorption in the open air is naturally very high. This, plus the fact that in some scenes there are entire trains powered across the stage by their own locomotives, creating unusually high background noise, requires high speaker output. With the action taking place all over the stage and with this high noise level it is impractical to use microphones on the stage. Instead all spoken parts are played in pantomime by the actors on the stage while their lines are actually being spoken by others located in sound-proof studios under the front of the grandstand where they can watch the lip movements of their counterparts on the stage and synchronize their voices to these movements. NO STAGE MIKES A picture of the central portion of the stage as viewed from the grandstand shows a scene representing a railroad passenger terminal. A pair of loudspeakers is mounted in the permanent sets on each side of the stage. A fifth speaker is concealed behind a gauze screen set into the center of the steps and beneath the elevated portion of the stage. A "behind the scenes" view of the pair of University Type WCC woofer-tweeter combinations is shown. Another backstage scene, this time looking from the wings toward the stage, shows (overhead) one of the several cuing speakers distributed around the sets and in the dressing rooms. The sound room in which all amplifier and control equipment is lo Here's one of the overhead speakers used backstage for cues. Top view shows the control console placed so operator can watch progress of the show. At right, another part of sound room, with the rack housing all amplifier equipment. cated, is so arranged that the operator can look through a window before him and watch all action on the stage. ONE CONTROL UNIT The control console on the table provides complete control of the entire installation, including volume level meters in the outputs of each of the five main circuits. Also shown is the 84-inch rack which houses all amplifier equipment including separate power supplies for the pre-amplifiers. Eight microphones are employed, each connecting to a corresponding pre-amplifier located in the lower portion of the main rack. The outputs of these pre-amps run to the control console where each feeds into an individual volume control circuit and an additional voltage amplifier. The outputs of these secondary amplifiers are grouped in pairs and fed into a series of push-button switches which permit the operator to switch any microphone, or group of microphones, into any desired combination of loudspeakers. This arrangement provided the utmost in flexibility of operation. A series of eight knobs on the console provide for gain control of the individual input circuits while the five large knobs at the bottom control the output of the individual power amplifiers (in the circuits of which the volume level meters are located). SEVEN AMPLIFIERS Following the console circuits are the power amplifiers. There are seven of these, each of the first five feeding one speaker. Number six is a bridging amplifier which drives a total of eight monitor and cuing speakers and seven is a spare which can be instantly substituted for any of the others by depressing two push switches and without the necessity for manually changing connection plugs, etc. The power amplifiers are the standard A-75-K "boosters," individually rated at 51 watts continuous output and 75 watts on peaks. Such great power is actually not needed but was provided for in accordance with the customer's requirements that amplifier equipment be such that it could be operated under extreme conditions and still provide complete assurance against breakdown, and also a maximum fidelity. EQUIPMENT ACCESSIBLE All amplifier and power equipment in the main rack is so mounted that the under-chassis wiring of each unit is accessible from the front of the rack by simply removing the corresponding panel. In the console all equipment is mounted on the hinged top panel and is therefore likewise readily accessible. All microphone and interconnecting cables are of the rubber covered and shielded two-conductor type. Speaker cables are for the most part run underground in lead sheathing and where above ground, are inclosed in rigid conduit. The speaker lines are all 500 ohms. Microphones are all Shure "Unidyne" low impedance dynamics, and the pre-amplifiers in the main rack are also low impedance. Monitor and cuing speakers are each equipped with individual local "L" pads so that the volume at each can be adjusted appropriately for its particular location and requirements. Sales Hints for Election Time "Immediate action" is suggested to sound men who want to get their share of "the avalanche of sound business that accompanies a national election," in a bulletin issued to Audiograph sound equipment dealers. Thirty controversial states, where the election outcome is most doubtful, are listed, and it is pointed out that dealers in these states should be doubly active. Five specific suggestions are made: (1) Contact the state central committees of each party, if you are near a state capital. (2) Contact the county central com (Continued on page 69) 45