Abstract: According to the invention, a high-powered community alerting and warning device comprising a number of electromagnetic drivers is energized for tone generation by means of a rotary alternator that produces, when driven at a predetermined rotational speed, a sine-wave a.c. in the 400-800 Hz range. The alternator output is applied directly to the drivers, eliminating costly amplifier modules and energizing the drivers for better efficiency and reliability than an amplifier system. The alternator can be the output of a rotary frequency converter, or it can be driven by an engine or a separate electric motor.

Abstract: The outdoor alerting and warning device of this invention comprises numerous electronic drivers and an axially shallow drum-shaped resonance chamber having an inside diameter equal to a whole-number multiple of one-quarter of the wavelength of a sound wave of predetermined frequency. The drivers are mounted on the exterior of the resonance chamber, on its peripheral portion at regular circumferential intervals around it, with their ports opening into its interior. A coaxial outlet port in one end wall of the resonance chamber, having an area of between one-half and two times the total of driver port areas, opens into the throat of a horn; or each end wall may have such an outlet port, each opening into a horn throat.