THE BRIDGE BROADCAST

Evening Star, Issue 21079, 16 April 1932, Page 4

THE BRIDGE BROADCAST

The broadcasting of the Sydney Harbour bridge-opening ceremony was notable for tTie fact that one microphone was sufficient for all the broadcasting, stations in Australia as well as a battfcry of public address loud speakers, talkie films, and gramophone records. The Bridge Celebrations Committee arranged that the control of the broadcast should be left to one firm, with the particular intention of avoiding the multiplicity of microphones which is usually a feature of a gathering of such importance. It was the task of the engineers to devise means to ensure a circuit from which all the broadcasting stations interested could take a “ split ” without reacting upon each other. A single microphone served for all the speakers at the official ceremony. The output passed into a two-stage amplifier placed under the dais, 'and from that point the service was split into eighteen channels. To each of these services a signal was given at a certain predetermined level of volume. Each station was thus in a position to amplify the service at a point behind the dais or to pass it on to its own studios for further control. Each station had a separate microphone at the rear of the dais, so that the announcers of the several stations could add special matter of their own choice upon the main service and,fade the latter in or out as they wished. The talkie companies were given an elevated position on the other side of the road, the wires to their stands running across the road in pipes which were covered with asphalt. In addition to the single microphone for the principal speakers, another microphone was situated in the corner of the dais for the Governor, who announced the various speakers. A third microphono was placed in a corner for the official announcer who described the proceedings. One of the “ splits ” served the public address system, a special amplifier being used which gave a sixty-watt undistortod output obtained from four power valves in push-pull circuit. These valves were fed from a pair of valves

in push-pull preceled by a single valve. The high tension for this amplifier was obtained by a pair of rectifiers. From the power amplifier twenty-five public address loud speakers were fed. These speakers were carried on electric light standards on the Bradfield highway and on Observatory Hill. As these speakers were dynamic they required field excitation. To accomplish this all the field windings were connected in series, direct current being obtained from the City Council’s mains, and broken down with carbon filament lamps. In Hyde Park there was also established a battery of six loud speakers on top of the public address vehicle. The whole arrangement passed off excellently.