[CAUT] Re: Temperature and pitch

[James Ellis]

Guy, let me try to clarify even more.  See my interspersed remarks below.

At 11:09 AM 3/3/05 -0700, Nichols wrote:
>At 11:35 AM 3/3/2005 -0500, you wrote:
>>Guy, Let me say it a different way, and perhaps that will clear up the
>>confusion.  I certainly don't want to mislead anyone.
>
>Hi Jim. Thanks for the prompt and complete reply.
>
>>Let's assume the piano is stable at a reasonable room temperature and
>>relative humidity, and the temperature is the same throughout the piano,
>>and does not change while you are tuning:
>>
>>1.  The temperature rapidly drops.  The strings cool faster than the plate,
>>and the piano goes sharp and out of tune because the strings did not all
>>cool by the same amount.
>
>Yup. Understood.
>
>>2.  The piano sits at the new temperature for 24 hours.  It will be back in
>>fairly good tune - not as good as it was before, but not bad either.
>
>"Fairly good", depending on the piano, and the bass won't be as sharp as 
>the plain wires, right? But... it will still be sharp, right?

No.  The piano has been at the new temperature for 24 hours, and nothing
should be sharp now.  It should be just about on pitch now.  It might be
just a tiny bit sharp, but not very much.
>
>>3.  The temperature suddenly rises to its original setting, and the piano
>>goes flat and out of tune.
>
>Flat..... compared to where it was (sharper than the original pitch), right?

No.  Flat compared to where it was, and flat compared to the original pitch.
>
>>4.  The temperature stays at its original setting for 24 hours, and the
>>piano will almost be back where it was before - not perfectly - but very
>>close.
>
>Yeah. "Mas-O-Menos", as they say down here. More-or-less in tune and at 
>original pitch after stabilizing at the original temperature.

Yes, that right.
>
>>5.  The temperature takes another abrupt rise, and goes above its original
>>setting, and the piano goes flat again and out of tune.
>
>Perhaps more noticeably out of tune with itself, especially the bass, right?

Yes.  By "out of tune", I mean out of tune with itself.
>
>>6.  The temp stays at the elevated setting for another 24 hours, and the
>>piano will be in fairly good tune again, and almost on pitch.
>
>You got me there. It seems that you are saying that the flatness due to the 
>elevated temperature is self-correcting with time. I've observed that after 
>24 hours the instrument will sound almost in tune with itself, but if the 
>temperature remains elevated and the piano equalizes at the higher 
>temperature, it will still be flat. Not, as you say, almost on pitch. A 
>rather predictable amount, actually.

Not necessarily.  It depends upon what the relative humidity is doing
during this time.  If it takes a nose-dive during this time, as it will
might, then you are right, the piano will remain flat.  If the R.H. remains
constant, which it won't, the piano won't be very flat.


>
>>7.  The temp suddenly drops back to its original setting, and the piano
>>goes sharp again.
>
>Sharp, relative to the "steady" pitch achieved after the previous
change/rest.

Yes, sharp relative to its "steady" pitch, and sharp relative to its
original pitch, assuming it didn't get all dried out.
>
>
>>8.  The temp stays at the original setting for 24 hours, and the piano is
>>almost back on pitch again, and almost in tune, but now it's ready for
>>another tuning.
>
>Yeah, if returned to original temp/RH, the piano should be near pitch and 
>not terribly out of tune, and definitely ready for a tweak or two.
>
>>All the temperature ups and downs have had their effect on the relative
>>humidity, and this has taken its toll on the soundboard.  It has also
>>worked on the various parts of the piano that don't all have the same
>>temperature coefficient.  All the while, the thing has been under tension.
>>And every time things moved at the bridge, tuning pins, etc, etc, it
>>actually slipped, and never quite came back to the same place as it was
>>before.
>
>Well, yeah! There are many other factors. Playing, especially rambunctious 
>playing, during the swings will have a randomizing effect on our 
>predictions. Also, if the RH changes little, in comparison to temp, and 
>there isn't a lot of play, I don't think we'll see too many changes due to 
>actual "movement" at the bridges, etc. The rate of changes due to RH swings 
>is much slower than that of temperature changes, also. The expansion 
>coefficient of the wires affects the tension in a very relative way, 
>dependent on mass, and in a direct ratio to speaking length, etc. Hence the 
>variations in the amount of pitch change observed in different sections of 
>the plain wires.
>
>>On the other hand, if you tune the piano while the temperature is changing,
>>you are going to end up with a botched tuning, especially if you are tuning
>>with an ETD.
>
>Ya' think? %^)
>
>>Does this answer your question?  If not, I'll try again.
>
>It clarifies what you have stated, I think.
>
>>Sincerely, Jim Ellis
>
>Thanks again for your reply, sir. I appreciate it greatly.
>
>Regards,
>Guy

Guy, I was not factoring in any playing at all - only describing what
happens as the piano warms and cools.  The humidity factor is much slower.
The temperature thing is immediate, and the point I'm making is that it has
to do with temperature differentials within the piano - the plate and
strings at different temperatures.

If you could plot the X-Y-Z coordinates of the piano's strings and
soundboard on a microscopic scale as it warms and cools, you would see
things moving around in all sorts of directions.  A simalar thing happens
with the soundboard as it gains and loses moisture.  Not only does the
crown rise and fall, but different parts of the board squirm around all
over the palce.  That's why the bass/treble will sometimes do a see-saw
effect if there is a big change in relative humidity.  

Jim Ellis