This is an old guide originally released in 1980. It presented the first good treatment of SOUND PROJECTION. It contains a mathematical formula for computing the calculated range of a siren.

In a nutshell, sound is measured in Decibels or dB for short. The greater the level of dB the louder the sound will be. According to the guideline, CPG-1-17, we must have a starting level of sound to begin our calculations. This level of sound is specifically determined by a SPECIFICATION that we must follow when we rate our sirens. Here’s a caution - we are NOT required to follow any specification when we rate our sirens. However, this specification establishes the starting point for the math. If we don’t follow the specification the math doesn’t work. Some makers of sirens clearly do not and in these cases you can’t use the guideline.

The starting point is determined by measurement of the sound level at 100-feet from the siren under strict compliance with the specification. The calculations state that whenever we double the distance we subtract 10dB, 10dB per distance doubled. For example assume we have a siren that is rated in accordance with the specification to be 100-dB at 100 feet. In this case at 200 feet (double the distance) we have 90-dB (subtract 10-dB), at 400 feet we have 80-dB, at 800 feet we have 70-dB and so forth.

According to the guideline, when we reach the 70-dB perimeter we have reached the EFFECTIVE range of the siren, in the above case that is 800 feet.

This is an old guideline but the math still works for open field coverage. There is a new and much better guideline.

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