21 LOUDSPEAKERS AND AMPLIFIERS USED IN PUBLIC ADRESS SYSTEMS AND ALSO APPARATUS FOR INTERCOMMUNICATION BETWEEN ONE MOVING VEHICLE AND ANOTHER AND BETWEEN A MOVING VEHICLE AND A FIXED POINT, SPECIFICALLY TRANSMITTERS, RECEIVERS, MICROPHONES, LOUDSPEAKERS, RELAYS, AND INDICATION LIGHTS, AND PARTS THEREOF, AND FOR ACCESSORIES USED IN CONNECTION THEREWITH