Solution to Tullahoma's Siren Flaws

[Whelen Rules]

You all probably know I have been trying to get Tullahoma's siren system upgraded to get a 70 dB warning in downtown for a while. I am planning to meet with the people in charge of the system to find solutions. The problem right now is downtown sits in a 65 dB zone, from the points of one siren at 1.24 miles from the center of town, another at 1.26 miles, and the last at 1.50 miles from the center. My proposal is to move the siren at 1.50 a little over half a mile down the road to provide downtown well withing the Vortex R-4 6,000 ft 70 dB range, and the at the points where the other 2 sirens meet will increase the dB by 3, so the city will have approximately 75-78 dB in downtown which will over come the near 65 to 70 dB ambient noise levels. So now all the inner city areas will have at least 70 dB and the more rural outer city area's will have 60-65 dB of warning. According to Whelen the Vortex R-4 has a range of 6,000ft to 70dB and 12,000ft to 60 dB. Thats all for right now, I will let you all know if I am successful.

[va_nuke_pe]

The 10 dB above background is typically misinterpreted. The background of concern is the frequency band in which the siren sounds, not the entire sound spectrum (16 Hz to 20,000 Hz octave bands). Most sirens sound in the 500 Hz octave band (that's 355 to 710 Hz, boys and girls - sorry 2001 and Modulator fans - they sound perdominantly in the 1000 Hz octave band which means that their sound is aborbed at a faster rate through the air hence reducing their range).

If you use a sound meter that measures in the octave bands (or 1/3 octave bands, no matter), I am sure that you will find that if you have 65 dB across the entire spectrum (sound in each frequency band is logarithmically additive to make the total SPL), you will likely only have 45 to 50 dB in the 500 Hz octave band. Hence, 70 dB in the 500 Hz octave band should be at least 10 dB above the relevant background noise.

Man-made noise tends to be in the 250 Hz octave band and lower (tires on the pavement, exhaust resonance, lawnmowers, 60-cycle hum from power lines) and natural noise tends to be in the 1000 Hz octave band and up.