|Company||Federal Signal Corporation|
The 500 Series was a line of electromechanical sirens produced by Federal Sign & Signal. It went through a lot of prototyping, ranging from a coded unit that allows it to make a "pulsed" signal, along with variants of single and dual tone models, even different phase motors were tested. They finally settled on one design that was compact, yet effective. This model unfortunately was advertised as a "mid-range" siren by Federal, which in turn caused their Thunderbolt siren to outsell it by a long shot. The most powerful unit they made was the 10/12 port, 3-phase 500SHTT, meaning single head two tone.
The 500-DHTT is a dual horn variant of the 500SHTT, they have 2 choppers and rotors each side, one being 8 port, the other being 12. They were offered with a 15 or 20 horsepower motor. Roughly 100 were ever made, and 7 units are known to exist as of 2018.