Sat May 20, 2006 3:35 am
Are the sirens directional or omni-directional? The circles method gives the estimated coverage for a single siren. It even works OK for a system of directional sirens when you take the union of the area coverage. However, the circles method is lousy for a system that uses a lot of omni-directional sirens because sound is logarithmically additive. How much louder? If you stood midway between two omni's that were equally rated, then the sound level when they were both sounding would be 3 dB higher than if only 1 were sounding. If you were in the middle of four of them operating, it would sound 6 dB louder than if any one of them were activated. 3 dB doesn't sound like much - but it corresponds to be 50% louder. 6 dB is 78% louder.