Radio today (Apr-Dec 1939)

Sound at *4 AbtM't f*k Network of 76 sound outlets provides regular program service. Centralized distribution gives unusual control. Unique installations in Perisphere and Lagoon of Nations. The almost miraculous accomplishments of Sound at the New York World's Fair are but a few indications of future sound developments. After hearing the successful application of sound, millions of persons will become "sound" conscious, thereby greatly increasing the demand for amplification in all fields. Soundmen everywhere can obtain tips from the installations at the fair. While a few of the features to be described are too complex for usual sound systems, simplified versions will find many applications. The sound system installed at the World's Fair will be capable of the simultaneous origination, monitor^ ing, volume control and switching of six independent programs, with separate distribution to four public-address channels and two radio channels. It will be capable of picking up either electrical transcriptions, radio programs, or remote pickups and will transmit these programs through the four studios to the 16 outlets on the Fair grounds, one of which is illustrated on opposite page. The Center is located in the Communications Building and consists of four studios and a master control room. The entire center is enclosed in glass so that it will also serve as a functioning exhibit. MASTER CONTROL A master control console contains all the operation controls for program selection, control, and the distribution to the sound system. There are five individual panels — one for program distribution, one for program selection and one for program control, plus an order wire panel and a secondary program distribution The program selection panel contains controls and indicators for an automatic pre-set relay system which permits independent switching to any of six program channels, and any of ten console input lines. The relay system is designed so that a desired program line may be pre-set on the controls prior to actual switching, without disturbing a previous input line which may still be in use and switched by means of a master key. The pre-setting and switching op Four speaker units are used in the lagoon for 360° stereophonic sound reproduction. A close-up of one of the 500-watt stereophonic speakers. High-frequency reproducers shown in upper section. Entire unit about 5 feet high used for low-frequency sound distribution. erations are entirely independent for each of the six channels. The grand master key provides for changeover of the desired channels simultaneously. "On" indicator lamps show on which line each channel is operating, while "Pre-set" indicator lamps show which line is pre-set. PROGRAM CONTROL The program panel contains controls and volume indicators for the six program channels. Each of these channels is of the bridging type, providing individual means for amplification, level control, level indication and monitoring The busses of four channels may be used to feed any combination of 50 P. A. program lines. These lines serve the various public address outlet stations at the Fair. Each of the 50 program lines has an individual control panel with a four-point selector switch for connecting it to Channels 1, 2, 3, 4. CENTRALIZED DISTRIBUTION CONTROL These panels each contain 2 5 individual P.A. outlet control panels. The total of 50 panels controls level and AC power to various remote P.A. outlets. A switch operates a relay installed at the sound outlets, opening the circuit when the pointer reaches zero. The relay turns off the AC to the equipment at that point. The output fidelity of the New York World's Fair sound equipment will be of the highest quality obtainable. The frequency response from the input of any console to the output is within plus or minus 2db. from 30 to 10,000 cycles without frequency compensations. The total harmonic amplitude distortion will be less than 1 per cent. Each P.A. outlet consists of a loudspeaker system and an amplifying system. The average length of the lines running to the loud-speakers is a mile and a half, and the longest distance is three miles. The volume of each loudspeaker of the various groups is adjustable by means of an individual volume control, recessed in the front panel. A typical outlet embodies two specially developed RCA cube loudspeakers driven by four 50-watt amplifiers. The new cube loudspeaker measures 36 in. on each side and contains separate low and high frequency driving units and an associated crossover network. Both units are of the permanent magnet type. The most spectacular aspect of the sound program at the New York World's Fair lies in the fact that for 46 RADIO TODAY