Electronic sirens

Claim 1

IN AN ELECTRONIC SYSTEM FOR CREATING AUDIBLE SIREN SOUNDS THE COMBINATION FOR OPERATING A SOUND PRODUCING TRANSDUCER COMPRISING, A PAIR OF ASTABLE TRANSISTOR MULTIVIBRATORS, EACH HAVING TWO TRANSISTORS AND EACH TRANSISTOR HAVING A BASE, COLLECTOR AND EMITTER ELEMENT, ONE OF WHICH MULTIVIBRATORS IS A BASIC OSCILLATOR, AND THE OTHER OF WHICH IS A CONTROL OSCILLATOR HAVING A VERY LOW FREQUENCY, LESS THAN THE FREQUENCY OF THAT OF THE BASIC, THE OUTPUT CIRCUIT OF SAID CONTROL OSCILLATOR HAVING CONNECTED IN SERIES THEREIN A SOURCE OF DIRECT CURRENT, A FIRST RESISTANCE, SAID EMITTER, SAID COLLECTOR AND A SECOND RESISTANCE, A PARALLEL PATH CONNECTED BETWEEN THE JUNCTION OF SAID FIRST RESISTOR AND SOURCE AND THE JUNCTION OF SAID COLLECTOR AND SAID SECOND RESISTOR INCLUDING IN SAID PARALLEL PATH A THIRD RESISTANCE AND A CAPACITOR, MEANS CONNECTING THE BASE ELEMENT OF THE INPUT ONE OF SAID TRANSISTORS OF SAID BASIC OSCILLATOR TO THE JUNCTION BETWEEN SAID THIRD RESISTANCE AND SAID CAPACITOR, AND MEANS INCLUDING SAID TRANSDUCER CONNECTED TO THE OUTPUT OF SAID BASIC OSCILLATOR FOR CONVERTING THE VARIABLE FREQUENCY OUTPUT OF SAID BASIC OSCILLATOR IN AUDIBLE SIREN SOUNDS.