tuben will be able to comment on this...

[iiipopes]

Better yet: calculate all you want to, then, as I have done, take a day to actually help an organ tech do his job and see just how far you really do move the tuning slides and how far the pitch really does change with temperature by actually being there with a tuning knife. Then take your micrometers, take a pipe, any pipe, out of its slot, warm it up with your hand until it speaks a quarter step or 50 cents sharp, then measure it however you want to. If you can actually discern a real difference in the dimension of the pipe more than the inherent accuracy/error limits of the measuring device, and can document it, I will personally send you a standard container of your favorite beverage equivalent to a case of domestic canned beer. Tuben speaks from experience, which is a far louder voice than all the math you want to shovel in.

[pgym]

Doesn't matter what temp you tune at: a change in temp from whatever temp the organ was tuned to will produce a change of length, ΔL = αΔTLo where α = the coefficient of thermal expansion of the material the pipe is made of, ΔT is the difference between the tuning and the target temperature, and Lo is the length of the pipe at the temperature the organ was tuned at.

Please do the arithmetic. CALCULATE how much the pipe changes in length when the temperature goes up by X degrees. And then, CALCULATE how much the speed of sound changes for the same change in temperature.

Now you are ready to CALCULATE the change in pitch due to the change in length, and the change in pitch due to the change in the speed of sound.

And then, you will know the truth, and the truth will be in you.

No. Temperature, density, and amplitude affect the speed of sound, but speed of sound is independent of sound frequency in non-dispersive media. For audible sounds, air is a non-dispersive medium, so variations in temperature and speed of sound are irrelevant to the sound's pitch.

[sloan]

No. Temperature, density, and amplitude affect the speed of sound, but speed of sound is independent of sound frequency in non-dispersive media. For audible sounds, air is a non-dispersive medium, so variations in temperature and speed of sound are irrelevant to the sound's pitch.

The first part is correct. Speed of sound is independent of frequency. That means that all frequencies travel at the same speed.

I believe the second part is incorrect, if the sound is produced by a vibrating column of air. If the speed of sound changes, the effective length of the pipe changes (faster speed = shorter column = higher pitch).

ONCE PRODUCED, the sound propagates through the air at a speed which is independent of pitch. That's not the same question of how the sound is produced in the first place.

At least, that's what Google reminded me tonight.

Let's see what Fletcher&Rossing have to say about Tuning, Temperament, and Temperature [of woodwinds, but this appears to apply to organs and brass] (p. 169-70):

"Another problem for wind players arises from the fact that the speed of sound increases with rising temperature. This means that a cold instrument will play flat, and its pitch will gradually rise as it warms up. This is, unfortunately, a drift in the opposite direction from that of string instruments, so that orchestras must take particular care with tuning. Another problem is that the warming of an instrument is uneven -- the upper bore near the reed will settle down to a higher temperature than the lower bore, and this gradient will vary with the temperature of the room. If the reed end is at about 35degC and the lower end at 20degC, the difference in absolute temperature is about 5% and the difference in sound speed about 2.5%."

to me, this says that ambient temperature affects the pitch of wind instruments by changing the speed of sound in the vibrating air column. Notice that they don't consider any change in the length of the air column itself.

Rising temperature makes wind instruments go sharp, precisely because the speed of sound changes significantly, while the length of the instrument does NOT change significantly.

[Todd S. Malicoate]

A simple solution for those playing with organs offered in the spirit of the season...

this common-sense method requires no special math, physics, or acoustics knowledge or ability...

this method will, no doubt, elicit just as many "it sounds fine" comments when asking others in your group about your tuning (even when you already know you were extremely sharp to the before-mentioned organ - one has to wonder why you would bother to ask in such a scenario)...

Get a tuning pitch from the organ and match it.

[Kevin Hendrick]

A simple solution for those playing with organs offered in the spirit of the season...

this common-sense method requires no special math, physics, or acoustics knowledge or ability...

this method will, no doubt, elicit just as many "it sounds fine" comments when asking others in your group about your tuning (even when you already know you were extremely sharp to the before-mentioned organ - one has to wonder why you would bother to ask in such a scenario)...

Get a tuning pitch from the organ and match it.

Bingo!

[Ken Herrick]

There is a "highly accaumed' DGG recording of the CSO doing a particular "organ symphony" which made me absolutely shudder when i listened to it.

The orchestra and organ were recorded seperately and the results were not good (IMO) as the discrepency in tuning was so severe.

Tuning an organ, or piano, or keyboard percussion, etc is not something which can be done in an instant by taking a "tuning note" from the head duck -oops, oboe, clarinet, electronic tuner, tuning spoon, etc.

"Tuning" is very subjective and is one of the things which, when done well, distinguishes a great performance from just so much more organised noise making. It, when well done, show one of the basics of good ensemble work - listening, co-operating, compromising, empathising and so on.

Any truly "professional" group would tune to the "fixed pitch instrument" and keep their ears open
all the time and adjust as needed to ensure a good performance.

As an aside, MY definition of a "PROFESSIONAL" is not a person who gets some financial, or other,
"REWARD" for blowing wind or scratching on strings, or beating on skins of dea animals; it is a person who strives to achieve the highest possible stand of performance for the pleasure of the "spectator, ie listener in the case of music, and works with fellow performers to ensure that those standards are met.

I have played with and conducted "amatuers" who put "PROS" to shame by making real music. It's a bloody good experience.