# Note Of Air Raid Siren



## Kai Stemm (Nov 3, 2017)

So I am curious as to what the note of an air raid siren is... I don't expect any of you to know this off the top of your head, and if you do that would be a little odd.
Anyway, as some of you know I play Bass, no not the flashy guitar, but the good old fashioned Double Bass. Anyway a friend of mine bet that I couldn't recreate a sound... I was intrigued and asked him to continue, long story short, I took him up on the offer, and I will be down a good tuner, and some rosin. (About $20) After some research, I haven't been able to find out the note, I know how to get the sound just not the note .
Any help?
Thanks
(Edit I'm pretty sure that it's a minor something)


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## mikewint (Nov 7, 2017)

Thought maybe someone else had more knowledge so no guarantees of correctness
Basically the tone is (music terminology) an Untempered (Just) Minor Third. In music the minor keys evoke feelings of sadness and melancholy. Untempered tones are based on the ratios 1:2 (octave) and 2:3. Unlike modern tuning wherein the 12 tones in a octave are equally (tempered) spaced.
Any way back to the siren. The WWII air raid siren consisted of an electric motor which was connected to two stators (rotating chopper rings) in which there were equally spaced slots cut out. The slots effectively cut the incoming air stream into chunks producing a sound wave. How many chunks depended upon the number of slots and how fast the stator was rotated.
In WWII Britain AC electrical current was 50 Hz this produced, in the motor used, a no load speed of 3000 RPM. In the US standardized on 60 Hz the motor would spin at 3600 RPM (no load).
One stator had 10 slots and the other had 12 slots thus producing frequencies (pitch) in a 5:6 ratio, the minor third.
When connected to the stators the motor's RPMs under load dropped to 2700 RPM and 3300 RPM respectively.
The frequencies produced are easy to calculate: England - 2700 RPM makes 2700/60 or 45 revolutions per second. With 10 slots in the stator we get 45 x 10 = 450 chunks of air per second or a frequency of *450Hz.* A very annoying harsh frequency at one time thought to actually be evil.
The second stator with 12 slots gives 45 x 12 = *540 Hz *
In the US the load speed is 3300 RPM giving 55 revs per sec and frequencies of 550 Hz and 660 Hz.
As the motor spools up and down the frequencies rise and fall. The volume of air drawn in determines loudness generally in the 130 dB range


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## vikingBerserker (Nov 7, 2017)

Ok, getting back to the question, I think it might normally be in F.

Get your bass and pull a siren video on Youtube for comparison.

Awesome about the double bass, that is one very cool instrument! I went from a electric bass to messing around with the double. When it comes to playing blues double is the way to go.

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## mikewint (Nov 8, 2017)

As above a mechanical siren is not in any sense "tuned" since it depends on the RPMs of the driving motor. As the RPMs increase so does the frequency PLUS we are also dealing with human perception of that frequency (pitch).
Without going into a lot of music theory the pitch of any instrument was by guess and by golly until tuning forks and Scheiblers tonometer. In 1836 he recommended that the A above middle C (piano tuned to the even tempered 12 note octave) be set at 440 Hz.
The French standard had been 435 Hz. In the US the 440 A became the informal standard in 1926. ASO adopted it in 1936. ISO adopted it in 1955 as ISO 16. It's pretty close to a universal standard though European concert orchestras will vary from 441 - 444 Hz
By that standard and following the 12 note even tempered scale: A = 440 Hz Bb = 466 Hz B = 494 Hz C = 523 Hz C# = 554 Hz D = 587 Hz D# = 622 Hz E = 659 Hz and your F = 698 Hz
The human ear is very sensitive to 400 - 500 Hz range and 450 Hz is annoying and even painful. Its even been termed evil. Professionally mastered music generally has its EQ curve start going down subtly at about 250Hz, hits a low between 400-500hz, and then slowly comes back up until it hits 2000-3000hz. Without that "notch" removed the sound is "muddy". Mixing programs like SoundForge have an EQ preset that slashes those frequencies.


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## vikingBerserker (Nov 9, 2017)

Boy Mike, I will say nobody Cuts-and-Pastes then claims the work as their own better than you.


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## mikewint (Nov 9, 2017)

Well don't know anyone here that does original research unless you do. All of the above is public record so unless you are stating an opinion you are at best paraphrasing what you read somewhere else. I am not a professional musician so did not have the note/frequencies memorized nor do I do sound mixing so that material was researched. Does that affect validity?

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## vikingBerserker (Nov 13, 2017)

Reading something and putting into your own words is one thing, cutting and pasting entire sections of somebody else's work and claiming it as your work is called plagiarism.


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## stona (Nov 13, 2017)

Frequencies of Musical Notes, A4 = 440 Hz

Gives the notes for particular frequencies.

I'm not sure that will get you close to an air raid siren. 

Cheers

Steve


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## mikewint (Nov 13, 2017)

stona said:


> I'm not sure that will get you close to an air raid siren.



Possibly, Steve but a mechanical siren is not "tuned" to a particular frequency as it depends upon the number of slots and the RPM of the driving motor. In general you want to keep the frequency in that 400-500 Hz range and produce a minor tone due to its psychological effect on humans.
In any case the tuning of musical notes is a bit arbitrary. Higher frequencies sound "brighter" so while officially, A = 440 Hz, orchestras will tune anywhere from 441 - 444 Hz and the 12 note even tempered octave is for the benefit of fixed-tuned instruments like pianos/organs. It makes changing the key of a piece a snap.


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