I know that my metal whistles play better when they are warmed up first and take that into account. However .. what I don’t know is what is going on with the metal that makes this necessary?
Jim
When you warm an object up, what you are actually doing is adding
energy to that objects’ molecules, so that they move faster. There are
many reasons this might help the whistle’s sound:
- When the whistle’s metal molecules are moving more readily, it is
easier for the whistle itself to vibrate. - The warm whistle will in turn impart energy to the air column inside
the whistle, making the gas molecules move more readily. - The increase in temperature changes the friction between the
whistle and the air, which might add some complexity to the sound…
But, I am not a physicist…
I cannot speak to the physics, but as far as how the whistle plays, when you warm a whistle, by warming the windway you reduce condensation when you play, making the whistle less likely to clog. Also, cold whistles (in fact, all woodwinds) play flat, so when you warm a whistle, you are bringing it up to pitch. Finally, some whistles simply need to be warm to play well: my Elfsong and my Burke WBB are two examples of whistles that don’t play well when cold.
–James
I think what James said about reduced condensation makes sense.
The reason a cold whistle is flat is because sound travels faster through warm air than cold. When the whistle is cold, it has a cooling effect on the air that you blow down the tube, though I can’t imagine it does so for long…the metal probably warms to your body temperature after you play for just a minute.
Personally I don’t hear any significant difference in the sound of metal whistles whether they’re warm or cold (other than that they’re flatter when cold), but I do notice a big difference in my wooden flute.
And the whistlesmith makes it that way on purpose, too. If he were to
make the whistle in-tune when cold, then it would be sharp when
warmed up, which would be bad if you play for more than 1 minute at
a time…
Well yeah, but I don’t think this is a conscious design feature on the part of whistle makers. The whistle warms up very fast, so if you’re checking the tuning it’s going to be warm.
Actually I bet the metal body warms up faster than the plastic head (talking about Generation-style whistles here), and since the sound is physically coming out of the head I guess that’s really what has to warm up in order for the whistle to be in pitch.
shrug Every whistle-making instructional I’ve seen specifically says,
“Before filing a holes into tune, make sure to warm up the whistle,
THEN test the hole’s tuning…” Seemed like a concious consensus to
me…
I don’t think the sound comes just out of the head, but also out of the first open tone hole.
But you are right: in my experience with both flutes and whistles, warming the head (or fipple) makes more difference than warming the body tube.
Probably my most dramatically difference instrument warm vs cold is my Elfsong whistle. Cold, it’s a beast: no resistance, no backpressure, takes more air than any Clarke ever made, and a cold, harsh, squeaky tone. Warm, it’s a beauty, with moderate backpressure, drastically lessened air requirements, and a lovely, complex sound, well balanced through both registers.
–James
Hi Jim
The metal in the whistle will expand as it heats up. This would mean that the the length of the whistle and the cross sectional area will increase slightly due to expansion, so this could affect the pitch as well.
David
Good point.
Also interesting observations about the fipple-end, guys…
I think if that were true, the whistle would actually get flatter as it warms, not sharper. I’ve seen lots of discussions about this for the flute, and the consensus was that any expansion would be so slight that it wouldn’t affect pitch.
James: I’m pretty sure the sound only comes out the head of the whistle. The open hole just vents some air and affects the length of the air column, but I don’t think there’s any sound coming out of it. I might be wrong though, I’ve never held my ear or a microphone up to an open hole on a tin whistle. 
Hi bradhurley
My first thought was that warming should flatten it too. I am assuming that the change in cross sectional area compensates for the flattening.
The relative change in cross sectional area would be higher for a soprano whistle than a flute due to the different sizes of the bore and possibly wall thickness.
Anyone out there with the measuring equipment to test this?
David
I agree that it makes sense intuitively, but as best I can remember from the discussions I referred to earlier (which involved a few instrument makers and a few physicists) the expansion would be no more than a few millionths of an inch at best, not enough to make a difference.
When my wife is cold… nevermind. 
From “Basic Calculations for Flute Making” that was posted some time back.
"Another very important physical quantity is the “cutoff frequency” fc.
This marks the boundary between low frequencies, which are reflected
by the tone holes back into the instrument to form strong resonances,
and high frequencies which leak freely out through the tone hole row.
The cutoff frequency also marks the division between the low-frequency
isotropic radiation pattern (energy radiates in all directions equally)
and the high frequency directional radiation patterns. "
A typical cutoff frequency mentioned was 1500 hz so most but not all the sound is coming out of the head.
Angelo
That doesn’t really add up. High A is 880 1760 Hz, so presuming the quoted material is correct (I have no idea, but it sorta makes sense acoustically) the higher frequencies would be only mostly overtones; the fundamentals would be “lower.”
Edited to fix transposition.
The fundamental and some of the overtones would be reflected back into the tube by the tone hole and the sound would come out the window in the fipple head. Part of the complexity of the sound is determined by which overtones are reflected and which come out the tone hole.
Angelo
Angelo, as I read what Daniel wrote and what you are writing I think you and he are saying different things.
Completely right. Go to any concert hall/gig venue/recording studio just before a musical event is about to take place and you will find players “warming up”. They are not only warming up their chops/fingers but their instruments as well. I don’t know the physics behind it but I can testify that when you and your instrument are warmed up, everything works much better. This translates to stringed instruments in that, if you get the wood humming, it is immediately more responsive. Same thing with drum skins etc.
Musical instruments know what needs to happen.
Musicians are crazed loons.
Amen to that chief!
My old Classical guitar knew just what to do when my ex used it to express her opinion of me one fine day: lots of noise and drama but no damage to the playing! One of these days I’ll get my head prints out of the back board 