Development of a vehicular directional siren with variable beamwidth utilizing a broadside loudspeaker array

A directional electronic siren was developed which could be electrically switched from a narrow beam in the forward direction for open‐highway usage to a broader beam for use near‐roadway intersections. The beam was produced by a vehicular‐roof‐mounted broadside array consisting of four compact commercial electronic‐siren loudspeakers spaced 15.2 cm (6 in.) apart. Two electronic systems were developed to broaden the inherently narrow beam of the broadside array. One system swept the beam from side to side in 1.4° increments. Another used a filter network to broaden the beamwidth by effectively changing the broadside array to an endfire array with asymmetrical phasing of the loudspeakers. A‐weighted sound‐pressure‐level measurements made in an anechoic chamber and outdoors on a vehicle show that the maximum forward sound pressure level of the directional siren was 8–10 dB higher than a single commercial electronic siren, and that the desired directionality properties were achieved.