"Resultant" tones caused by dual-toned sirens

[Robert Gift]

In designing sirens, is the purpose of two tones to produce a "resultant"
tone"?

With two tones sounding simultaneously, their sound waves will add (reinforce) and subtract (cancel) at various frequencies.

For example: sounding an E-natural and a G-natural (a perfect minor third above), as in the 2t22, produces a resultant tone of C-natural (3 steps below the E natural)

Notes C + E-natural (a MAJOR third apart) produce a G-natural
(four steps below the C)

The same happens with organ pipes.
To produce very low pedal notes (which you may feel more than hear) without building the huge costly pipes necessary, organ builders will often create a "Resultant" stop, which sounds a note a fifth above the Unison note.

For example: if a C-natural pipe (produced by a 16 foot long pipe)
is sounded with a G-natural above (produced by a 10-2/3 foot pipe)
their resultant frequencies produce a low C @ 32' pitch length (an entire octave below the 16 foot C).

Has anyone made a dual-toned siren with notes a perfect fifth apart?
Such would synthesize a note a full OCTAVE below the lower of the two notes.

Since low tones carry farther, is the dual-toned siren made for that purpose?

In some siren recordings, I perceive the single resultant pitch more than the two actual tones creating it!

Thank you,

[ronatello]

I too have observed that phenomenon when listening to the various siren videos w/ dual tone sirens (the T-bolt in particular). And yes, you can simulate lower tones by combining two other tones. Take for example, the pipe organ. Play the C1 (let's say the C1 of this organ is around 32.5 Hz) and the G1. Of course, temperment has some to do with this as well. If tuned to perfect 5ths, when you play the C1 and G1 notes, you can "hear" (or I should say, you feel) a C0 note around 16Hz. This can be done with the organ tuned to equal temperment but the results when tuned to perfect 5ths will be better.

The ASC T-135 or ACA P-50 has this phenomenon as well .I hear a note just below middle C, roughly 250 hz. What is the port ratio on the T-135, 8/12? If it is dual toned at all?

Most of the T-bolt videos out there have a T-bolt blasting away with the low note around C# and the high note around E. When you combine these two, you get a Bb note.

[Robert Gift]

I too have observed that phenomenon when listening to the various siren videos w/ dual tone sirens (the T-bolt in particular). And yes, you can simulate lower tones by combining two other tones. Take for example, the pipe organ. Play the C1 (let's say the C1 of this organ is around 32.5 Hz) and the G1. Of course, temperment has some to do with this as well. If tuned to perfect 5ths, when you play the C1 and G1 notes, you can "hear" (or I should say, you feel) a C0 note around 16Hz. This can be done with the organ tuned to equal temperment but the results when tuned to perfect 5ths will be better.

Are you also an organist?
Thanks for the octave IDs. I never know what to call C1.
Never heard of a C0.

You are correct about the tempered 5ths.
Some organ builders borrow the 5th's from another, or same, rank of
pipes. But being tempered (which means they are slightly narrower than
perfect or pure fifths) makes the resultant out of tune - but still close.

The ASC T-135 or ACA P-50 has this phenomenon as well .I hear a note just below middle C, roughly 250 hz. What is the port ratio on the T-135, 8/12? If it is dual toned at all?

Wish I knew. I'm still a novice. Don't know about different sirens.

Most of the T-bolt videos out there have a T-bolt blasting away with the low note around C# and the high note around E. When you combine these two, you get a Bb note.

Exactly.
Is there a reason for that, such as furthering sound propogation?

In organs, I've always wondered why not make one 32' pipe instead
of a 16' plus 10-2/3' to produce that 32' pitch?
Seems it would be easier and cheaper. Well, you would only be
using 26-2/3' feet of wood to produce 32' pitch. But making two pipes;
mouths, languids, feet, etc. seems a lot of work instead of one.

I am impressed with how the siren starts to sound even when turning the
rotor by hand. The chopping of the air is amazingly efficient/productive.

Thank you,

[SirenMadness]

Yes, the T-135 has an eight-to-twelve port-ratio.

[STHboy]

This is an interesting topic - I had noticed that sound in recordings of dual-tone sirens, notably the one of UVFR's SD10. You have to listen closely to realize that the siren is producing a fourth interval, not an octive between the high tone and the resultant tone.

But you really have to get close to a siren during an activation to get the full experience of the resultant tone (and everything else, of course.) When I recorded the Allertor in Central Park in St. Paul, I had no clue how much the resultant tone affected the entire tambre of the siren. From 2-3 football fields away, the resultant low tone really shook the ground! You won't hear it in my recording, of course - maybe you will, but it's nothing like being there.

[ronatello]

Are you also an organist?
Thanks for the octave IDs. I never know what to call C1.
Never heard of a C0.

You are correct about the tempered 5ths.
Some organ builders borrow the 5th's from another, or same, rank of
pipes. But being tempered (which means they are slightly narrower than
perfect or pure fifths) makes the resultant out of tune - but still close.
(rest snipped)

I'm not an organist but I've read up on pipe organs some, thanks in part to my love for them. I play piano but not very well yet . But C1 is what I refer to the 1st C on the keyboard. If the very large pipe required to sound the super low C (16 hz) isn't available, then one can play C1+G1 to get the "C0" note.
Resultant tones can be facinating to say the least

[Daniel]

I am an organist also, and have noticed this "resultant" effect in various sirens. I mainly study bells, which have several prominent tones to listen for, but I've noticed that certain dual-tone sirens have a greater resultant effect than others, even among sirens with the same port ratio.

The first 2T22 I had heard was about a mile away, and with the D and F notes it created (not exactly those notes, but close enough for the topic), there was an almost-audible Bb note resulting. In fact, at first I thought there was another 8-port siren sounding with it. A 1003, though, has a much stronger overtone with the same minor 3rd interval, possibly due to it's forced-air design or the shape of the horn or ports.

Sirens have been created in 2nd (Federal 76/77 vehicle siren), major 3rd (Model 2T, Hurricane), neutral 3rd (some HOR Super Sirex), minor 3rd (2T22, 1003, Carters/Klaxon), perfect 4th (5T, Banshee, Allertor), flatted 5th (some HOR Super Sirex), perfect 5th (T-135, Cyclone, Sentry 40V2T, some Decot), 6th (some Decot), and octave (most Sterling/Sentry models) intervals. The perfect 5th comes in 8/12 (ACA models) or 10/15 (Sentry). Running any siren on a 50 Hz. supply drops the pitch by a major 3rd.

One subject I would like to see discussed is the relation of the shape of ports to the siren's timbre: square, rectangular, elongated rectangular, trapezoidal (see avatar), slanted, or even round (IMI from former DDR).

[Robert Gift]

I am an organist also, and have noticed this "resultant" effect in various sirens. I mainly study bells, which have several prominent tones to listen for, but I've noticed that certain dual-tone sirens have a greater resultant effect than others, even among sirens with the same port ratio.

The first 2T22 I had heard was about a mile away, and with the D and F notes it created an almost-audible Bb note resulting. In fact, at first I thought there was another 8-port siren sounding with it. A 1003, though, has a much stronger overtone with the same minor 3rd interval, possibly due to it's forced-air design or the shape of the horn or ports.

Sirens have been created in 2nd (Federal 76/77 vehicle siren), major 3rd (Model 2T, Hurricane), neutral 3rd (some HOR Super Sirex), minor 3rd (2T22, 1003, Carters/Klaxon), perfect 4th (5T, Banshee, Allertor), flatted 5th (some HOR Super Sirex), perfect 5th (T-135, Cyclone, Sentry 40V2T, some Decot), 6th (some Decot), and octave (most Sterling/Sentry models) intervals. The perfect 5th comes in 8/12 (ACA models) or 10/15 (Sentry). Running any siren on a 50 Hz. supply drops the pitch by a major 3rd. Seems like a lot of drop until I realize it is 5/6ths of the frequency.

Wow! Dan, thanks for all that fascinating information!
I shall copy it onto a page when I get back to Denver.
How do they derive a "flatted fifth"? I used to tune and I can't remember
is tempered 5th narrower (flatter) than pure? Tempered 4th wider?
Hey, I even tuned our cuckoo clock pure! Next, our wind chime.

My electric shaver sounds a step lower here in Yantai, China.
220 50 Hz.

One subject I would like to see discussed is the relation of the shape of ports to the siren's timbre: square, rectangular, elongated rectangular, trapezoidal (see avatar), slanted, or even round (IMI from former DDR).

Yes. I've always wondered what partials port shapes will cause.
Like those in your photo.
Also, I'd like to hear/feel what a rotor/stator chopping water (completely
under water, SLOWLY wouldo.)
See my Yantai posts if you wish.

[Conky 2000]

And also, you know those Sentry Siren videos where they test the sirens in the garage? Well, if you watch the 40V2T video, that has this same phenomenon that happens after the windup. Just like the P-50/T-135.