Dual-Toned Sirens

[adtbolt07]

Ok, before I ask this I would like to make this point clear: Dual Toned sirens, especially the Thunderbolt 1000T, are by far my favorite, so I am in no way implying that I think dual -toned sires are pointless.

I believe that the federal government originally, in the early years of the cold war, mandated that sirens purchased with federal funds be dual toned. Why was this, and what was/is the point of a siren being dual toned rather than single toned? Is it only becuase a dual toned siren sounds better/more distinct?

[Melvin Potts]

I recall reading something about this many years ago.

If I remember correctly, the reason for being dual toned was to distinguish the air raid/civil defense siren from the single tone fire sirens used by many communities.

[StonedChipmunk]

I recall reading something about this many years ago.

If I remember correctly, the reason for being dual toned was to distinguish the air raid/civil defense siren from the single tone fire sirens used by many communities.

This seems plausible. I believe dual-toned sirens don't have much of an advantage in terms of volume and distance - in fact I think dual-toned sirens have a generally lower output.

Dual-toned sirens do seem more distinct than single-tone, though. I'm going to agree with Melvin for this one. It could also differentiate between civil defense and fire engine sirens (which, I believe, were mostly mechanical back then).

[Daniel]

Dual tone sirens are only underpowered if they have a single, two-level rotor like the Model 2T where the ports are half as tall as the regular Model 2, or in a situation where one row of ports is starved for air due to poor construction. A Model 2T has a lower decibel output than a Model 2, and I'd think that the same would be true for a dual-tone Banshee or Screamer. Dual-rotor sirens like Sentry dual-tone models are louder than single-rotor sirens of the same rotor size, since both rotors have equal intake capability.

[Archon]

Not all Cities had Dual tone CD sirens some had single tone
Example

Milwaukee Had a system of model 2's and I mean a lot of them too
St Louis had STL's as did San Francisco.
Chicago had TB 's and a lot of STL's

[kagome122885]

Dual-tone sirens also have a wider frequency range than single tone sirens.

[Daniel]

Dual-tone sirens also have a wider frequency range than single tone sirens.

This is particularly true if the interval between the two pitches creates a resultant third pitch. Often it is this resultant pitch that commands the most attention over ambient noise. Dual-tone Thunderbolts, because of their unusual construction, have a raspy-sounding low resultant pitch that sounds something like an old three-port Elektror fire siren.