Physics of organ tuning

[soundboarddude]

I was reading an encyclopedia article on electronic organs, and it mentioned hybrid instruments, and why they must be tuned.

The frequency of sound produced by an organ pipe is determined by its geometry and by the speed of sound in the air within it. The speed of sound changes with the temperature and humidity of the air; therefore the pitch of a pipe organ will change as the weather changes, so the pitch of the digital side in a hybrid instrument must be retuned as needed.

Dumb question:
Does the temperature and humidity of the air cause the pipes to expand and contract, causing the slide or scroll to move? I had always thought that this was due to temperature, not so much humidity...

[Guest]

Re: Physics of organ tuning

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[KleinErzahler]

Re: Physics of organ tuning

Greetings,

Wood pipes can be sensitive to humidity but in a different way; the depth of the windway changes from winter to summer and back. The character of these ranks can change quite considerably in certain instances. Sometimes the caps will loosen up during low humidity as well, which will make the pipes either breathy or unable to tune sharp enough.

Best,

- N

[soundboarddude]

Re: Physics of organ tuning

Facinating! Thanks for the replies. I figured it was something along those lines...

I'm curious as to how Rodgers can do that. Do they simply measure the humidity of the air and the temperature where the pipes are and calculate the pitch? How interesting!

Heck, why am I having to tune the organ every week if we've already got the technology that can do it for me? *grins*

[Guest]

Re: Physics of organ tuning

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[RW]

Re: Physics of organ tuning

Changes in the dimensions of flue pipes due to variations in temperature and humidity have only a minor effect on pitch. Rather, it is the temperature of the air that causes the greatest change. Warm air is much more dense than cold air, and the density has a direct effect on the weight of the air column within the pipe. In dry air, the change is approx. 1.7 cents per degree farenheit, or about a quarter semitone per 15 degrees. The effect becomes slightly greater as the humidity increases. Because of this, an organ should always be tuned at the same temperature that it will be when the organ is used.

[Guest]

Re: Physics of organ tuning

Reeds are much less affected by temperature changes than flues. The dimensions of the reed determine the pitch (primarily), the resonator, which is affected by the air density, less so. Short resonator reeds are almost unaffected by temperature. Trumpets (full length) are somewhat affected. If the temperature changes too much, the pitch matching between the resonator and the reed becomes too much different and the reed will fly off speech.

More information can be obtained from E.M. Skinner's book.

Note that the Rodgers only needs to sense temperature to adjust the electronic tuning. When tuning my pipe organ, the tuner always checks the chamber temperature prior to using an electronic tuner and adjusts the tuner pitch accordingly. I have installed a chamber heater to maintain a constant temperature for the pipe work so that the tuning is pretty stable.

Too much temperature fluctuation will cause some tuning slides to slip and an occasional pipe will not return to the proper pitch. I suppose that this is the reason some new baroque organs still use cone tuning since the pipe work is exposed to the ambient environment..

[radagast]

Re: Physics of organ tuning

>I do know Rodgers has a nifty automatic tuner that detects when the pipes tuning change, and tunes the digital voices accordingly. I think it's kinda neat.

I am pretty sure that Allen also has some method of keeping the pipes and digital voices in tune on a pipe/digital hybrid. Hybrids would be a nightmare without something like that.

[Havoc]

Re: Physics of organ tuning

I played on an old hybrid about 20 years ago. That was still analog circuitry with tubes. And even that had a (manual) tuning knob.

[Guest]

Re: Physics of organ tuning

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[Guest]

Re: Physics of organ tuning

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[soubasse32]

Re: Physics of organ tuning



French reeds are not necessarily more prone to pitch problems. I have a feeling you have been listening to recordings of French organs? If so,the out-of-tuneness you may hearhas more to do withhow often organsin French churches get tuned.

Or, the season the recording was made...

[Guest]

Re: Physics of organ tuning

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[soubasse32]

Re: Physics of organ tuning



Well perhaps a thinner tongue might be more prone to disturbance...

But I don't think it follows a nationalistic pattern [:D] unless French reeds use thinner tongues.

I think a lot has to do withhow organtuning budgets are managed and the availability of tuners in each country.

Oh one other thought - French organs have many batteries of reed stops; Pedal reed stops are often independent. With all of those reed pipes, there's bound to be some that are just "out" on any given day!

[Guest]

Re: Physics of organ tuning

And, perhaps the French reeds start to sound out of tune quicker, is because those nasel overtones simply exaggerate the out-of-tuneness. I play on a French Romantic Casavant down here, and, it is rare that it sounds perfectly in tune, because the reeds are so firey and nasel.