PRESTRESSlNG APPROACH TO PITCH LOWERING


Piano tuning has been established as a specialty occupation for over 130 years. Now, more than any other time in our history, rapid and basic changes in other fields are having massive influences on piano tuning.

In the last decades  we have seen the superfast tuner, the precision approach to pitch raising, inordinately accurate tunings, the advent of inhumanly accurate electronic tuning aids, and a better approach to scaling pianos -just to mention a few.
In the next years, we will be modifying many of our approaches to tuning, rebuilding, and resealing. We will see an ever-increasing demand for accuracy by ourselves, of each other, and by the buying/owning public. Competition will become stiffer – especially for those who do not keep abreast of what is happening and who do not incorporate the new and superior methods.
It is the philosophy and intent of this blog to present the more suitable, the improved, the new, or even the novel way that is in keeping with good craftsmanship and work habits. It is the further intent of this blog that such methods mentioned are in agreement with the best practices of piano-tuning.
PRESTRESSlNG APPROACH TO PITCH LOWERING
We might tend to assume the aural art/science that we practice has not developed much in recent years, but one has to admit that the art of aural tuning is still developing.
In keeping with that thought, let me now outline the procedure I have developed to rapidly “prestress” the scale prior to fine tuning when lowering pitch. Let’s change the wording of the familiar old shoe, “You cannot fine tune an out-of-tune piano,” to read, “You cannot fine tune an out- of-balance piano scale.” Since a fine tuning is also a delicate balancing of the scale’s tension, any rapid method of achieving a close approximation of that balance prior to the fine-tuning sequence would be of great benefit.
Suppose a particular piano is 8 cents sharp (i.e., A442), and it must be tuned to A440 for a concert. The iron plate and the soundboard crown would not be offended, if we lower the pitch of every other note 16 cents (twice the required amount) to pre- stress the scale prior to tuning every note. Carrying this logic a step further, the plate and soundboard still would not be offended, if we prestress the scale by lowering every fourth note 32 cents to save time (four times the required amount). However, we discover that, in doing so, the whole scale creeps back up a bit and we have not quite accomplished the desired purpose. I have discovered that lowering one additional note per octave four times the required amount compensated for this scale rise.
Let’s suppose the piano to be tuned to A440 is fairly in tune with itself, but at a pitch of A442. First, drop the entire F3-F4 temperament octave to A439.5 and clear the unisons. (The slight undershoot will creep back up to approximately A440 as we proceed.)
Next, skip F#4 and G4 and insert a rubber mute between the centre and right strings of G#4. Sound the G#3-G#4 octave and listen to the beat of the 2-1 partials. In this example, the beat will be about 2 bps. Lower the pitch on the left string of G#4 and invert the beat. (The term “invert the beat” means to change the beat so that it is the same beat but in the opposite direction; i.e., if it is 2 bps sharp, “invert the beat” so that it becomes 2 bps flat.)
Now, insert the rubber mute between G#4 and A4, then play the note G#4. The beat of the fundamentals between the left and centre strings should be approximately 4 bps. Invert the beat by lowering the centre string of G#4 so it now becomes 4 bps flat to the left string. After lowering the left and right strings to the centre string, we have doubly inverted the beat of note G#4. When sounded, the G#3-G#4 octave should have a 2-1 beat of about 8 bps.
Do the same to 64, D5, and F5. These four notes (G#4, B4, D5, and F5) now comprise the “prestressing temperament” for the remaining treble notes. Tune pure octaves as you proceed to G#5, B5, D6, F6, G#6, B6, D7, F7, G#7, and B7; the entire top half of the scale is prestressed for the A440 level.
Proceed downward into the bass section in the same manner, doubly inverting the beat of D3, B2, G#2, and F2; Tune pure octaves for D2, B1, G#1, F1, D1 and B0; the entire scale is prestressed for the A440 level.
After the 13 notes of the temperament octave are set, the procedure takes about 3 minutes to prestress 24 notes and is considerable faster than dealing with all 75 remaining notes before beginning the second time around the scale.
As we proceed up and down the scale and away from the temperament octave on our second time over the scale, we can determine if our pre stressing procedure was properly done if the “ups” balance the “downs.” For example, as we proceed upward this second time from the temperament octave, if we lower F#4 and G4 a couple of beats, and are still in balance if we raise G # 4 about four beats, etc., then our prestressing procedure is correct. Of course, this is only a rough comparison because the actual beat rate would change according to the degree of original out-of-tuneness.
Anyone who starts to use this procedure will find that, as they familiarise themselves with this valuable new method, they will develop a sense of when they are “right on,” so to speak. My way of looking at prestressing is not as a time-saver, but rather as a method of producing a finer final result in the allotted time. In most cases, a three-timesover tuning will have a slight edge over a two-timer. Since our 3-minute prestressino counts as the first time around, we can still accomplish the second time around after that, and all three trips fit nicely into the allotted time. I am sure that you can adapt all this to the temperament octave of your choice.
I am certain that there are individuals reading this prestressing procedure who have already deduced that it also can be used to increase scale tension slightly, and that the term “invert the beat” can go in both directions. After much deliberation, we have decided to present the procedure in terms of pitch lowering only. Persons who choose to investigate it in any other manner are strictly on their own.
The idea of prestressing began to knock around in my head several years ago, and I have used the procedure in the form presented here for a couple of years now.  
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