[CAUT] pre-stretching new string Wet vs Dry Soundboard

[Don]

Hi Fred,

I agree about a plethora of factors.

RCT does not use "calculated figures"--but Chameleon 1 did rely on actual
physical measurments of the strings to generate a tuning "chart". It still
exists in the windows laptop version of RCT but may not be used very often.

My historys with FAC readings generally became lower over time with repeat
tunings to A440--unless there was a spike (either up or down) in humidity
levels. Then "all bets were off". I never analysed them for "trends".
Unfortunately I no longer have the data to work with.

For what ever reasons I generally do not find stored tunings satisfactory.
Nor do I enjoy "machine" unisons. 

All I am offering is my observations in a very general and non scientific
way. Humidity control works--it would be nice to know why and how--seeing
as apparently most of us have been wandering down a "garden path" rather
than the real world.

At 04:09 PM 6/10/2007 -0600, you wrote:
>On 6/10/07 7:21 AM, "Don" <pianotuna at accesscomm.ca> wrote:
>
>> Dean Reyburn's first efforts to generate tunings relied on measurements of
>length and
>> diameter of strings. The generated tunings were then uploaded via a midi
>> cable to a SATII.  They didn't always “fit” the piano.
>
>    Were the differences between calculated and real life tunings due to
>differences in humidity (equilibrium moisture content) and its effect on the
>board? I guess that's one speculation. I don't know if it's true. Seems like
>there are a plethora of factors that could and would contribute.
>    The RCT doesn't use calculated figures from length and diameter, but
>rather empirically gathered figures: partial ladders of the As, read
>directly. Then each A is set according to the "pre-sets" or the "Custom EQ"
>(based on the partial ladders) and notes between are entered according to a
>mathematical curve. There are a couple additional algorithms for the tenor).
>There are often occasions where a partial or more in those ladders appears
>somewhere it shouldn't be according to an even curve (predicted value). I
>thought _that_ was what Dean called para-inharmonicity.
>> 
>> It is also why “stored tunings” don't work well in areas where humidity
>> changes by more than a few percent.
>
>    I've read statements to that effect. I'm not sure it's true. The
>assertion is that real life inharmonicity readings (on which the FAC and RCT
>calculations are based, using slightly different means) vary with humidity.
>I have looked for a pattern and haven't found one. Have you? Has anyone? If
>so, what is the direction and size of the change? From, say 20% RH to 60%
>RH, does the A number increase or decrease? By how much on average? (On RCT,
>compare the figure in the tuning spreadsheet for G#4 to get a rough
>equivalent of the A number difference in FAC for SAT).
>    I've certainly seen variance in readings, but no pattern with respect to
>RH. The largest differences I've seen are before and after tuning (same
>day), occasionally a change of 2 cents and more for that A number (or G#4 on
>RCT), always downward after tuning. I speculate it is due to output of the
>board being influenced by the vibrational modes of the strings: more
>synchronicity, leading to more coupling of partials. Just speculation, and
>if anyone else has a different explanation, I'd like to hear it.
>    In my own experience, stored tunings work just fine in an environment
>varying from under 10% to over 70% RH. Never had a complaint, never noticed
>a problem. Has anyone else? In which case, what was the problem? More
>precisely, in what direction was the problem? Dry to wet, which "wants
>narrower octaves" and which "wants wider?" (If you stored the tuning when it
>was dry, did it produce octaves that were too narrow or too wide when wet,
>and vice versa?)
>> 
>> I believe that some SAT users have documented inharmonicity tends to lower
>> over time when a piano is kept “at pitch” as the strings conform to the
>> bends in their length at the capo bar and the bridge pins.
>    Somewhat similar to what I describe above. I'm not sure what the
>mechanism would be from "conforming to their bends." Do you read higher
>inharmonicity on a newly installed string which has had no "massaging"
>compared to one that has? I can't say that I have measured that, myself.
>Regards,
>Fred Sturm
>University of New Mexico
Regards,
Don Rose, B.Mus., A.M.U.S., A.MUS., R.P.T.
Non calor sed umor est qui nobis incommodat

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