Second-interval siren in Portugal

[Daniel]

Here is a classic Portuguese siren sounding a very long fire call. These are 10/11 sirens (or perhaps 11/12) that resemble a British siren but sound a second interval instead of a minor third. These seem to be common in Portugal but I don't know if they are found elsewhere, like Spain.



https://www.youtube.com/watch?v=wjirMDJlw7Q

[holler]

Sounds like a two speed motor.

[SuperBanshee]

A very interesting siren and fire call pattern.
Very few dual tone sirens used the 2nd interval due to the overlapping frequencies of both tones. Sirens with both tones moderately separated across the octave scale fared best at long range distances. Tones separated too close or too far result in an overlapping effect which hampers sound output. This is why nobody makes anything like a 5-15 blade siren.

The most efficient dual tone intervals for sirens were the 4th (9-12 or 15-20), Perfect 5th (8-12 or 10-15), and Minor 6th (10-16). They all hit the "sweet spot": not too far, yet not too close.

[holler]

10-12 does pretty good, at least on the xt22. They really have some range for just a 10 horsepower siren.

[SirenMadness]

I really dig that close ratio, it definitely ranks up there on the scale of creepiness.