System for selectively operable dual simultaneous siren broadcast from a single speaker

A sound communication system comprising:

• a first modulating oscillator having a first output lead, said first modulating oscillator producing a first signal on said first output lead thereof;
• a second modulating oscillator having a second output lead, said second modulating oscillator producing a second signal on said second output lead thereof, different from said first signal;
• a first voltage controlled oscillator (VCO) having a first input lead and a third output lead, said first VCO producing a third signal on said third output lead;
• a second VCO having a second input lead and a fourth output lead, said second VCO producing a fourth signal on said fourth output lead;
• a loudspeaker having an input lead, said first output lead being connected to said first input lead, said second output lead being connected to said second input lead;
• and means connected from said third output lead and said fourth output lead to said loudspeaker input lead for impressing a signal upon said loudspeaker input lead directly proportional to the sum of said third and fourth signals.