Tuning a piano to a pipe organ
Today I finished tuning the Moller Pipe organ at my church. It is a 3 manual organ plus pedal with 46 ranks. I started out in the pipe organ business and many piano technicians are unfamiliar with matching the pitch of the piano to a pipe organ. Pipe organs are very temperature sensitive. For every one degree of temperature change there is a corresponding change in pitch of 2 cents. If an organ is 5 degrees cooler than it is used for services it will be 10 cents flat from where it was tuned. When you consider that a rank of pipes for manual stops contains 61 pipes and most pedal ranks contain 32 pipes you can see that the number of pipes in a large instrument outnumber the numbe of strings in a piano. With that being the case it is easier to change the pitch on the piano to match the organ rather than the reverse.
A piano technician must insist that the temperature of the room be set the same as it was set when the organ was tuned or there can be no guarantee of matching pitch accurately. The stops that should be selected to check the pitch should be from the Principle or Octave family. Flutes such as Bourdons, Wald flutes, Gedeckts and the like are not a good source from which to compare pitch. Never use a Celeste stop as they are intentionally tuned sharp to the rest of the organ in order to produce a tremolo effect. One should also make sure that the Tremolo stop is not on when trying to match pitch. Reed pipes such as Trumpet, Oboe and Clarion stops can be unstable and should also not be used for a pitch reference.
A piano technician can either read the pitch of the Tuning stop on the organ with an electronic device or can match pitch aurally by having someone hold the appropriate key down on the manual. I have wedged a pencil between the back of the key and the nameboard on many occasions then walked back to the piano and matched the pitch to get started. Once you have a pitch reference tune your regular temperament and tune the piano in the usual manner. Because of the difference involved in the creation of tone organs do not provide stretch in the manner of stringed instruments. The end result will be two different instruments with a basic starting point that is the same. There will be differences at the outer ends of the registers but they will blend well together.
Norman Cantrell, RPT