Sedgwick county kansas goes with ATI.

[Melvin Potts]

The San Francisco ATIs have been mentioned here. I thought about something related to them. If I understand correctly, they play recordings of the old STL-10s. Even though the STL-10s are no longer made, I wonder if Federal could've gone after them for patent infringement, etc.

Many of the S.F. ATIs are mounted LOW. The one at Union Square is mounted on the remains of an STL-10. When I was on the upper deck of tour bus I could almost stand up and touch the speakers.

[coastalsyrolover]

Yes they do. And what makes it more interesting is the fact that the ATI is OVER 20 DB quieter than the actual STL-10. And they honestly do a horrible job at playing the recording back... I have heard a real STL-10. Sounds way better.

[dclarkct]

If ATI uses off the shelf drivers (if, because I don't know) they are designed for PA use not siren use. Run a square wave into a PA speaker and you can burn them up real fast.

it isn't the fact that it's a square wave, it's that the power being delivered to the speaker is more than it can handle. for example, lets say you have an amplifier which can supply 100 watts into an 8 ohm load. If you drive this amplifier to its maximum unclipped output with a clean sine wave, that means it will be applying 40 volts peak to the speaker. A sine wave has a crest factor (ratio of peak to RMS) of 1.414, so the speaker is getting 28 Volts RMS. So, power being v^2/R = (28.3)^2/8 = 100.1 watts continuous. A 100 watt speaker that is truly capable of handling that will be fine.

now, if you take the same amplifier and drive it so far into clipping that it's sending a square wave to the speaker, you're still only applying 40 volts peak to the speaker. However, the crest factor of a square wave is 1, so the speaker is now seeing 40 volts RMS. Which means (40)^2/8=200 watts. Your 100 watt speaker will burn up.

However, if you use a 200 watt speaker, then the amplifier above should be able to force-feed it square waves all day. Most police/ambulance electronic sirens use square wave signals (I know for a fact at least Federal and Whelen do.) They just make sure to use a speaker designed to handle twice the rated RMS power of the amplifier so the speakers survive.

Absolutely right. The crest factor for a square wave is 1. so when you calculate the power you need to make sure the speaker is rated for that power. also the speaker is on and off at fairly low frequencies, the speaker coil acts like a heater coil and soon the magnet structure will be very hot. Whelen has invested lots of money in a custom design that will last a long time. There are high temperature components (diaphragm, capton former, high temp solder) these components allow the driver to survive constant use to hours of continuous activation. Sorry if this sounds like a sales pitch, I am only reporting what I know because I have had to test it. I also do not try to trash any other manufacturer I am only pointing out what Whelen does. :thup:

[floor-a-matic]

Why didnt they go with:
Sentry
3V8H
10V2T
20V2T
16V1T
40V2T

Federal
Eclipse8
508

ASC
T-121
T-135

At least all of the above have battery backup capability

[carexpertandy]

The 3V8H, 10V2T and 20V2T are only AC capable. With ASC, you forgot to mention the T-128.

[TboltTX1]

Why didnt they go with:
Sentry
3V8H
10V2T
20V2T
16V1T
40V2T

Federal
Eclipse8
508

ASC
T-121
T-135

At least all of the above have battery backup capability

Because $$$.