Multi-speaker electronic sirens often are alleged to have dead spots at certain angles to the vehicle's direction of travel. These are caused by phase differences. The sound coming from the speaker array can phase cancel in some situations. This phase cancellation occurs at single frequencies, based upon the spacing of the speakers. These phase differences also account for increases, based upon the frequency and the speaker spacing. However, sirens are designed to sweep the frequency of their sound output, typically, no less than one octave. This sweeping minimizes the effects of phase cancellation. The end result is that the average sound output from a dual speaker siren system is 3 dB greater than a single speaker system.