This article originally appeared in Horn & Whistle Magazine, Issue #41.
Reprinted here courtesy of Horn & Whistle Magazine.

The illustrated page shows some past and present motor driven sirens. Many of you have surely seen most of them at one time or another. Within a 25 mile radius of me, I know of at least seven different types in use today. Usually they are installed at Fire Houses and they alert for fires, emergencies, and as a 'noon whistle' signal. Common sirens in my area are Figure #10, the Federal STH-10, 10 horsepower. Among the towns having one are Ripley, NY, Maplesprings, NY and Mayville, NY. Fig. #5, the Sterling Model M, S or 10 HP dual harmonic tone. Findley Lake, NY has one of these. Figure #9, the Federal Thunderbolt 10 HP. The city of Erie, PA has several of these around town for what I believe is Civil Defense. A volunteer fire department near Erie also has one for their alarm. Figure #11 shows one of the sirens that is of unknown manufacture to me. Two fire departments near Erie have one each of these. If anyone knows the manufacturer of this siren, please let me know. Figure #12 shows a Harrington Model 2V8. Ripley, NY has one of these out on the west side of town to reinforce the coverage of their main Federal STH-10.

Figure #2 is the A.C.A. Cyclone 50 HP. This is the most powerful omnidirectional siren available, rated 125db at 10⁰ feet. Fig. #4 is the A.C.A. Penetrator 50, 50 HP rotating. This is the most powerful siren available today, rated 135db at 100 feet. Figure #1 shows the King of all the motor sirens, the most powerful sound signal of all time, the Chrysler Air Raid Siren, out of production today. Powered by a 180 HP Chrysler hemi-head V-8 engine, it delivers an incredible 138db at 100 feet. That's twice the power of the most powerful siren of today, the ACA Penetrator 50 (for each 3db increase in output, the sound volume doubles).

For anyone who is not familiar with what a siren is, it is an air chopper. The sound is created by a stream of air being cut by a slotted rotor, which spins inside of a non-rotating slotted cylinder. When the stream of air from the compressor passes between the slots in these two components, it is chopped by the high speed spinning rotor; this creates the sound. The principle of generated sound is different than that created by a diaphragm horn or whistle.

The identifications of the sirens illustrated on the following page are:

1. 180 HP Chrysler.

2. A.C.A. 50 HP Cyclone, dual tone.

3. A.C.A. Hurricane.

4. A.C.A. Penetrator 50, 50 HP.

5. Sterling Model M, 5 or 10 HP dual tone.

6. Sterling Model 5V.

7. A.C.A. 2 to 10 HP Screamer.

8. A.C.A. 10 HP Allertor.

9. 10 HP Federal Thunderbolt.

10. 10 HP Federal STH-10.

11. Unidentified. (Federal SD-10, 10 HP)

12. Harrington 2V8.

13. Sterling Model 10V2T.

There are of course a lot more sirens than shown here. These are probably some of the special or more well known ones. Numbers 2, 5, and 13 are dual tone and produce an harmonic sound.