How to Achieve a Stable Tuning

I recently submitted this post to the PTG discussion page. I thought it appropriate to add to my blog, since stability is such an important skill. Look for a book and video course on the subject soon.
Mark

Posted on ptg.org:

I don’t use test blows. I planned on using them on my RPT exam but forgot. I passed anyway.

Why I don’t use them:
– Too hard on my ears.
– Too hard on my arms, hand, shoulders, next, etc…
– Too hard on the piano.

I use a method I call Non-Speaking Length Tension Analysis.

I teach piano tuning so I need a method that makes sense and people can understand.

Here are the concepts:

TENSIONS
Speaking Length Tension (SLT): Tension in the speaking length of the string
Non-Speaking Length Tension (NSLT): Tension in the string on the tuning pin side of the v-bar/agraffe

Intuitively, we understand that for stability, we need

SLT = NSLT

However, because of friction, there is a “band” or “range” of NSLT’s that produce stability. Some people call this the “Marshmallow Zone”.

Intuitively, we understand that NSLT should be in the middle of that band.
With experiments, I have shown that, for stability, the NSLT should be slightly higher than the middle of the band, to account for the rise in SLT during hard blows.

BENDING/TWISTING
During tuning we have bending and twisting.
After tuning we have unbending and untwisting.
While raising pitch (clockwise), the NSLT is at the top of the stable tension band or range.
While lowering pitch (counter-clockwise), the NSLT is at the bottom of the stable tension band or range.

The change in NSLT brought on by the unbending and untwisting that occurs after we remove our force from the hammer, must leave the NSLT slightly high of middle for stability to be achieved.

TECHNIQUE #1:

Slow Pull
Untwisting always moves the NSLT toward the centre of the band.
Examples:
Raising pitch – clockwise – NSLT at top – untwisting is counter-clockwise and reduces NSLT.
Lowering pitch – counterclockwise – NSLT at bottom – untwisting is clockwise and increases NSLT.

Unbending adds or subtracts to the NSLT depending on the hammer angle and the length of the non-speaking segment. (Short segment tensions change more for the same unbending, than long segment tensions do.)

Example:
Raising pitch at 3:00 (upright)
During tuning, bending is downward, toward string.
NSLT is at the bottom of the range of stable NSLT’s.
After tuning, unbending is upward, away from the string, thereby increasing NSLT.

With practice, the tuner can discover hammer angles for each piano and area of the piano where a slow single pull to pitch and the subsequent unbending/untwisting, will result in a stable NSLT.

TECHNIQUE #2:

Pitch Window

For a given tuning pin foot placement, there is a range (window) of pitches that are stable. If one tries to affect a given pitch that is outside this window, the pitch will be unstable and drift back into the window during hard blows, or after time. This can be shown by using excessive bending to change pitch and observing how unstable that technique can be.

Pitch Window Method
1) For a given tuning pin foot placement, gently massage the pin toward the string. This must be a very gentle massage not intended to change the pitch. If the pitch doesn’t change, the foot placement is a stable one for that pitch.
2) If it does change, the pitch was not stable for that foot placement, but this new pitch is. This can be proven by repeating the same gentle massage. The new pitch will not change.
3) If the pitch was desired and then changed, the foot must be moved clockwise, and the massage test done again.
4) If the pitch was too high before the massage test, hopefully this new pitch is good.

So, in essence, the procedure is:
1) Assess pitch
2) If it is correct, apply the gentle massage test. If the pitch passes the massage test, great. If it doesn’t (i.e. drops), move the foot clockwise.
3) If the pitch needs to go down, apply the massage test. If the pitch goes down, great. If is doesn’t, move the foot counter-clockwise and retest.
4) If the pitch needs to go up, move the foot clockwise and apply the massage test.

Notes on the Pitch Window method.
– The tuner must be able to change the foot placement as little as possible.
– The amount of force used in the gentle massage test is variable. Experience shows us how much is too much or not enough.
– With experience, a massage up technique can be used as well.

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