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coastalsyrolover
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Re: Thunderbolt Siren Coverage Area

Mon Sep 07, 2015 8:06 am

DJ2226 wrote:The simple answer is that there is no defined dB rating, and it varies from unit to unit.

When CD was still a thing our city got ratings from FS&S and FS. Those didn't list the 100' SPL, but the 70 dB range which is more important with any siren. They rated them, at that point in time Series A2 or B 1000ATs with 5/6 port choppers at level 6 and 4M blowers, to have an effective coverage radius of 4500'. They had the same ratings with the older units with the 5M blowers. Swapping the blowers around yields a slightly louder siren, but from what I've heard in person I couldn't tell the difference, 5M vs 6M. I've actually heard some that in some instances the 4M blown siren would be louder even with the blower not forcing as much air as the 5M

Now these sirens could vary in pitch, so as you change it you'll change the SPL of the siren and the way the sound propagates. For example a 1000 putting out 575 Hz will carry differently than if the same siren was putting out 485 Hz. You can see this on the electronic side with Whelen. The upped the pitch of their sirens to 560 Hz from 435 Hz (455 and 530 Hz were also used on that controller) making sirens like the 2910 and 4004/Vortex R4 jump from 126 dB to 129, and I can tell you from personal experience that it makes a big difference with our 2810s and some of the Vortexes over yonder. With that said even when the siren could produce different pitches while sustaining volume theoretically (Thunderbolts are technically louder higher pitched as more air can flow through the head, I've heard this in person) the change in pitch dramatically changes the performance. This is why Whelen tests their sirens in alert to get those ratings, and it is also the reason the Equinox and 508 will perform the same, if not better, then the 2001-130 even though they're "quieter."

The main mechanisms I've seen that effect the way sirens perform are atmospheric absorption and ground impedance. The first one is the basic one, where the higher the pitch, the fast a sound will be absorbed into the air the second one is the absorption and scatter of sound along the ground. It's lowest at 500 Hz and stays constant as you go from 500-1000 Hz. It acts like the graph of a polynomial function with the leading coefficient's exponent being even and positive, makes a "U". 500 Hz is the sweet spot for sirens, although you could make the argument that it blend in too much with the environment. I mention this because of the dual tone vs singe tone mentioned above, but from a different perspective with the cancellation stuff aside. In this case with a 5/6 port 'bolt running at chopper level 6, half, give or take, is making ~ 575 Hz and the other ~ 690 Hz. The high tone side of the siren is absorbed into the air faster.

Even though it's kind of off topic, there was mentioned a Thunderbolt being heard from 9 miles away. I've heard a 2909 from about 10 miles away when I was recording one of our sirens. That was the closet one on Ft. Benning, GA to where I was. Pierce Chapel Rd. in Columbus, GA and 11th Airborne Rd./Moye Rd. in Ft. Benning, GA
Nice! 10 miles! Thanks for the explanation. Makes a lot more sense. I have noticed that the higher pitched thunderbolts seem a bit louder too. Especially at a distance. Carrying wise it kind of depends. The Yakima one has been said to have been heard from about 10 or so miles as well... But I would like to hear that for myself. Furthest I have actually seen (In the video above) was 9. Anyways though thanks again for the explanation. I will go ahead and stop spamming this thread now :lol: I just love the Thunderbolt.
Own and love a Thunderbolt 1000 and a Model 5.

I have many hobbies and interests. And I love them all.

Christian, Lima, Oscah, November, Golf.

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FahmiRBLX
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Re: Thunderbolt Siren Coverage Area

Thu Jun 21, 2018 9:09 am

Sorry for derailing, but how much dBs 1000T &1003s make with no blower, and how much Decibels each variant of all the Thunderbolt's and Hurricane's blower add to a 1000T & 1003?
A Muslim Malaysian, a siren & aviation enthusiast, and gamer.

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