Has anyone ever made triple-toned sirens?

[Robert Gift]

Also, does dividing the rotor air into two tones slightly lessen the sound output compared to having larger stator ports producing one tone?

[Justin]

I have not heard of a tri-tone siren as of yet.

Dual tone Thunderbolts are rated at 125dB @ 30m, single tone Thunderbolts are rated at 127db @ 30m, so splitting the chopper does have an effect on the output rating.

[Robert Gift]

Thanks Justin.

Sorry to learn that, but expected such.

[Justin]

Anytime, mate

[SirenMadness]

Dual-tone sirens with one are indeed quieter because the ports on the rotor and stator are smaller than ports on a single-tone rotor, and one of the rows of vanes on a dual-tone rotor will have to be smaller, to allow a sufficient flow of air to the row of vanes below.

I do remember that there was a siren which allowed for a set number of rotors to be added to it; the siren was made by the Cosgrave company. It was a single-tone siren, though. I can't remember its biggest acceptance for the number of rotors.

[Robert Gift]

I can't remember its biggest acceptance for the number of rotors.

You could stack more rotors and stators to make it louder?
Or was it to add additional tones?

How interesting if the latter.
I'd love to play with something like that - trying differentone combinations.

[ronatello]

Having 3 discreet rotors / stators would probably be the best option if one were to make a tri-tone siren, IMHO.

[Daniel]

One of our newer visitors from England mentioned that four-tone sirens may have been made in the UK during the war, possibly a Carters with dual-tone heads at each end. I don't know whether these actually existed, but if one were built and operated on 60 Hz. current with a 3,450 RPM motor, a siren having a port ratio of 6/8/10/12 would conceivably generate a 2nd inversion Bb major chord (F/Bb/D/F). In the UK on 50 Hz., it would be a 2nd inv. F# major chord.

With regard to dual-tone sirens, if there is only one rotor, there is generally a loss of output compared with an equivalent single-tone siren, i.e. Model 2T versus Model 2, because each segment of the dual-tone rotor is half as tall as the single tone rotor. A twin-rotor siren like the 2T22 will actually be louder than its single-tone version, the STH-10, because it has two heads, and two heads are better than one.

[SirenMadness]

I can't remember its biggest acceptance for the number of rotors.

You could stack more rotors and stators to make it louder?
Or was it to add additional tones?

How interesting if the latter.
I'd love to play with something like that - trying different tone combinations.

You add rotors, and possibly even the stators too, to supposedly make the siren louder. I think that you'd attach the rotors to one-another by their flanges.

[SirenSteveUK]

I have only ever seen two 'four-toned' sirens in the UK. One was at Tangmere RAF airfield (long since removed) and the other may still be in position near Bournemouth (as I noticed it after our air raid siren cull). Will have to dig into my notes and then go and investigate to see if its still there. From what I remember, the Tangmere siren was of WWII vintage but the Bournemouth one was more recent - which suggests it wasn't a one-off prototype. The ends of the siren did not taper which suggest it wasn't a Carters siren modification, though many companies made different siren types during WWII in the UK.