Over the years a number of fascinating articles have appeared in The Diapason on the subject of organ reeds. Not withstanding a few of my own, I would like to draw attention to the excellent contribution of Roland Killinger in 1977, entitled "Reeds with Short-Length Resonators."This entertaining description of the vagaries of reed construction and tuning was presented to the American Institute of Organ Builders by Mr. Killinger, who was at that time, in charge of the Sueddeutsche Orgelpfeifenfabrik in Freiberg-Beihingen, Germany. Jan Rowland prepared a translation which appeared in The Diapason.
Because the subject of the article was half-length reeds, Mr. Killinger brought up many points that had to do with the specific study of resonance in slider and pneumatic windchests. These observations on resonanance are applicable to full length stops as well as fractional length stops. I believe that a discussion of resonance for full lenth conical stops such as trumpets and half length cylindrical stops such as clarinets is long overdue.
The photo of John Brombaugh blowing his horn was taken in 1992 at the symposium on The Historical Organ in America, held at Arizona State University. In a presentation on reeds, Brombaugh made one point: that reeds ought to be tuned at the point of their natural resonance. To prove it, he took a reed pipe out of pocket and demonstrated how to find the "flip point."
Finding the flip-point of a conical stop
When tuning a conical stop it is easy to find the nodal resonance or flip point. One tunes to the correct note, then sharpens the note at the tuning wire until the reed jumps approximately an interval of a third. There is no "squeezing"it up to pitch, a reed pipe will suddenly make the leap, seemingly on its own. This indicates the presence of what Roland Killinger calls "resonance points"or "optimum tuning points."They are the points around which tuning is most stable and the resonance between the tongue and the tube of the pipe is the most pronounced.
Once the tuner has determined the point that the pipe "flips"or jumps to the first harmonic above its natural resonance point, it is a simple matter to flatten the pipe until it "jumps" back to its fundamental pitch. Once it has done that, another principal may be observed.
With the pipe speaking its fundamental pitch with a rather "close"tone, one may observe that if the pipe is covered, it will jump back and remain at its first harmonic. However, if the pipe is made to speak again, it will return to the fundamental. The resonator is telling the tuner that it is too long. In most conical reeds, the point at which this behavior stops and the pipe will no longer jump to its harmonic by covering the resonator is the point at which the fullest and most pleasant tone is achieved. It is the point of the most natural resonance between tongue and resonator. It is also the point of the most stable tuning, because the air column in the tube has the most telling effect on the vibrations of the tongue. In other words, they are vibrating together, rather than the more common situation where the tube is merely amplifying the vibrations of the tongue. That is the difference between an auto horn and a trombone or French horn! So it is with organ pipes.
The old masters of organ building knew these rules and built reeds of great power that not only resonated with themselves but with the flues of the organ by vibrating through the slider channels so that the reeds exercised a drum like effect on the principals of the organ. The whole organ was a marching band!
Applying the rules of resonance
Organ tuners can check the "flip"point of virtually any reed, whether conical or cylindrical. If the point of natural resonance is sharp of normal pitch, one will note that as the reed is flattened, it will lose its round and full tone and gain a rather grating, nasty sound which is actually less powerful than the point of natural resonance. Reeds which speak on the short side of natural resonance do not exhibit stable tuning, since they are inclined to find a nodal point which is no where near the frequency to which they are actually tuned. This is a chaotic situation and leads to frequent tunings and unhappy organists. All tuners are familiar with organs that require tuning immediately before a performance to ensure any consistency at all. And how many tuners sit through concerts wondering when this or that note will take leave for a walk on the wild side!
Correcting short resonators
Once short resonators have been found by checking the "flip" point and determinating the pitch where the best tone is found, a simple paper extension may be made to lengthen the resonator to its normal acoustic length. Heavy packing tape works well, and may be applied to "chorale"a wandering reed. The improved tuning stability will be well worth the time spent legnthening resonators, even on a temporary basis. Most organists will hear the difference and set about raising the money to solder a new length to short resonators and repair flaps that have been rolled down in a vain attempt to stabilize tuning. Once accomplished, the organ tuner will experience a much deserved rest, and the organist will find the reeds much more satisfying to play.
