FahmiRBLX

I hope no one give me more rep for now, until like mid- or late-August. It's 550 and I'm gonna go back to making a few siren replicas.

For those who are wondering, inrroducing Federal Signal 550. Or Federal Signal 500-DHTT if that makes more sense among siren enthusiasts.

The two-horned version of the 500-SHTT.

Decommissioned Cold War era unit in Los Angeles, California.

4-bar unit in Reedsburg, Wisconsin. Both the Thunderbolt 1003 (same manufacturer as the 500) & 500 has been replaced by a model 2001 from the same manufacturer as of 2020.

6-bar unit in... I don't know, I'm no American.

Narrow-horn unit, second pictuee in Dundee Township, Michigan. First picture, I believe is the same unit taken more recently. Now is inactive and moved somewhere as a decoration as of 2019.

So Federal made lots of design changes to the 500 siren (while the 500-DHTT or 550 is a different variant, but doesn't fall under the "design changes" category). All types of horns came in with two options; one with a single-tone chopper & stator^[1], and one with a dual-tone chopper & stator^[2]

Footnote:

[1] This is what 'true' sirens (i.e Mechanical Sirens, aka "air raid siren", "old siren") make sound with. A motor spins the Chopper really fast, air gets forces through the chopper and escapes once the holes on the Chopper & Stator line up, hence making a sound. The faster it spins the louder the sound & higher the pitch.

[2] Two sets of chopper & stator with different number of holes the more the holes the higher the pitch, but sometimes the quieter the sound due to less air getting through.

[3] There are two types of sirens; Mechanival & Electronic. I've explained the Mechanical one earlier, now the Electronic one. The Electronic one should be the easiest to understand; it's a loudspeaker that plays siren tones.

[4] Any type of siren can be an air raid (or war in general), nuclear (both power plant & fallout), tornado or tsunami siren. It depends on which emergency does that siren warns of.

[5] Ever heard about the Chicago's sirens? It's not broken at all, it's a signal called "Alternate Wail". It's essentially the "Wail" everyone's familiar with typical air raid sirens, but with the "Hi-Lo" of a British police siren mixed into it. The result, a High-and-Low tone that is also a Wail in the same time.

EDIT: Photos aren't mine, credits to the original owners.