Speaking Walls.

Kaipara and Waitemata Echo, 1 May 1914, Page 2

Speaking Walls.

By means of an ingenious electrical device, passengers at the New Grand Central Terminus at New

York are informed of the forthcoming departure of trains in a manner that makes it appear as though the walls were speaking. Thirty-six megaphonic transmitters are hidden ill the walls of the various rooms of the station. These are operated by only one announcer, who talks in an ordinary tone into a single transmitter at a central point. The transmitter is surrounded by a water jacket through which a tiny stream of cold water flows constantly, cooling the carbon, which would otherwise become packed with the heat of the heavy current of 110 volts used in operating the announcer. The ordinary telephone requires only a small fraction of this amount, but it is through the employment of the heavy voltage, says the "Popular Electricity Magazine," that the remarkable results are obtained. The voltage is so equalised, and thi^ circuits so balanced, that the sound of the human voice is intensified many times. And there is no limit to the number of points to which wires may be run for the transmission of sound from the central point.