[CAUT] Wire Stretch

[RicB]

Hi again Fred.

Interesting reading to be sure. I have virtually no experience with 
Everetts, 1098's and Hamiltons so I will have to simply acknowledge your 
observations and ponder how / why / what the frig now !  on them.  I 
agree 100 %... we are really shooting in the dark and probably will 
continue to for a long time given the fact that it actually takes quite 
a bit of resources to start solving this particular puzzle.

My exercise goes along the lines of simply identifying one particular 
factor in this whole scheme.  Namely what bearing strain results from a 
given change in deflection.... all else being left alone.  Strikes me as 
being worth while to take into consideration, along with knowing just 
what the structure is capable of in the first place when considering all 
this.  Which brings me to the question.... just how much <<pushing 
power>> does a "typical" soundboard assembly have ?  How many pounds can 
one actually expect a panel assembly to be able to hold up to begin ?  
Put into the perspective of how much the thing can change vertically 
unloaded .... well.. at least one can see some limiting parameters this way.

Cheers
RicB


    On May 3, 2007, at 11:00 AM, RicB wrote:

         > Hi Fred.
         >
         > I have never seen a piano behave like this in 30 + years of
        working 
         > on them.  There is always a major shift at each break in the
        scale. 
         > Most times one can even see a slight jump even when the scale
        is 
         > broken/widened at the front termination and not at the bridge.  
         > I've watched pianos very closely for a long time relative to 
         > climatic changes, and what I see is a similar type of
        movement in 
         > each section.  If the lowest part of the tenor is sharp
        relative to 
         > the rest of the tenor section... then you see the same thing
        in the 
         > tenor/treble break... and the treble/diskant break (up to the
        last 
         > highest octave)  and in the bass section.   Same thing in
        reverse 
         > if the low tenor has become low with respect to the rest of its 
         > section.  The pattern is nowhere near as severe in the bass or 
         > highest treble (diskant)... but its there.  I dont think I have 
         > ever seen an exception to this <<rule>>.
         > The only part of the piano that doesnt seem to fit into this
        is the 
         > highest octave...especially from F-G7 upwards.  Seems to do
        what 
         > the low tenor is doing and seems to have a very large reaction.


    Hi Ric,
        Well, I have observed this repeatedly on the Hamilton 243s,
    Everett 
    studios, and a couple Steinway 1098s I service regularly. There is a 
    gradual increase in the pitch change from about C6 (which is at about 
    "high average" pitch), rising logarithmically to C8. I have found as 
    much as 75 cents on the top few notes, with tenor change being in the 
    25-35 cent range. Of course, as I wrote earlier, this seems to be 
    "model specific" to a large extent. I don't see it at all in Yamahas, 
    for instance, where often areas in the high or mid high treble can be 
    sharp when the rest of the piano is flat and vice versa.
        There's also a quirk to the 243s at the treble break. The pitch 
    change accelerates as you approach it from below, then there is a 
    sharp jog of less change for the first few strings above the break. I 
    attribute it to something to do with scaling and tension, as a guess. 
    Virtually every other piano behaves as you describe above, with 
    mirroring jogs at each break.
        In observing this kind of thing over the years (getting to be 
    decades, now), I have found that the data can often be contradictory 
    and confusing (especially if you don't know intimately what has 
    happened to RH in the interim between tunings). I have often intended 
    to start documenting (as in actually writing things down), but the 
    times when the data would be most useful tend to be the times I am 
    utterly swamped and can't spare the time. So I rely on memory, and 
    make short notes in my work log. For instance, I have recently taken 
    to writing "RP 5-25 cents, -50 cents HT" to show that I raised pitch 
    in most of the piano 5-25 cents, but the high treble was as much as 
    50 cents flat. I have found myself doing this notation a good bit the 
    past few years, and wonder why I didn't notice it years earlier. (I 
    used to distinguish the bass, but stopped bothering. Actually, 
    though, there can be a good bit of variety there as well, from not 
    much change at all to quite significant - again, probably model 
    specific).
        Until a large range of data is collected, very specific as to
    model, 
    humidity history between tunings, and with samples at a good 
    representation of notes, we will be making stabs in the dark. And one 
    would also need to know at least something about bearing and crown to 
    make it really worthwhile. I'm sure my own particular climate affects 
    what I observe, as does yours. I don't get quite the extremes Mark 
    Cramer and others in the frigid north get, but I do get single digits 
    regularly, and up to 80% RH. 10 - 60% annual swing is pretty average. 
    I suspect 40 - 90% would give markedly different results, for instance.
    Regards,
    Fred Sturm
    University of New Mexico
    fssturm at unm.edu
    -- 


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