Abstract: An electronic siren apparatus has a primary horn with a throat which splits into matched secondary horns each having sides, an output end, a longitudinal axis, and a circumference. The secondary horns are folded back toward and around the primary horn and throat and the portions of the circumference of each end are joined. The folded secondary horns and the joined portions form a cavity which houses the primary horn and throat. A driver is operatively joined with the throat and is contained within the cavity for generating sound which is transmitted through the throat and primary horn, and then into each secondary horn and out the output ends in phase and amplitude matched relation. The area of the primary horn and the combined areas of the secondary horn, satisfy the equation ##EQU1## where x is the distance measured along the axis from the throat, cosh is the hyperbolic cosine function, d is the diameter of the primary horn and the combined diameters of the secondary horns, d.sub.