No downbearing ? REVISITED

[David Skolnik]

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David Love -
Thanks for responding.  I haven't forgotten that you started all this with=
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your Negative Bearing question a few years ago.  Let's see if I can keep=20
this on track long enough for me to understand.  To simplify things a bit,=
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can we agree to acknowledge, then ignore the fact that we cannot determine=
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the original bearing set up from measuring the strung piano? Why does there=
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appear to be this growing consensus that these "after stringing"=20
measurements are deceptive, confusing, and of no value?  Whether or not the=
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board is being compressed  (i.e. stiffened) by one area of the string=20
scale, if I get readings showing zero or negative downbearing in a section=
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of the piano, is it to be dismissed because there is downbearing SOMEWHERE=
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on the board?

With regard to transfer of vibrations, can you, David, or anyone else,=20
direct me to recent discussion that supports this view of the irrelevance=20
of downbearing in this process?  (I will scan the past years posts if you=20
cannot.)  If such is, in fact, the case, and if you could create the=20
hypothetical soundboard with sufficient stiffness WITHOUT employing=20
downbearing's compressive function, is there, in your opinion, ANY aspect=20
of the mechanical transfer of energy from string to bridge ( & board) via=20
bridge pin, that would suffer in the absence of such downbearing?   For=20
example, if the string were to traverse the bridge, captured by the pins=20
(horizontally) , but at 1/16th or 1/32' above the bridge surface?
And what is the nature of the coupling you speak of? (Bridge translating=20
string impulse)  What is the implication regarding the way the string=20
energy transfers from string to bridge to board?  Did I miss the resolution=
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to that question?  Sorry for all the questions.

David Skolnik





At 07:25 AM 1/30/2004 -0800, you wrote:
>The transfer of vibrations happens due to the coupling of the string to=20
>the bridge, not due to any downward pressure of the strings onto the=20
>bridge.  That coupling is achieved by the interlocking of the string=20
>through the bridge pins .  Whether or not you have downbearing will not=20
>influence this coupling.  The downbearing effects the amount of downward=20
>pressure on the soundboard.  When the board is compressed it gets=20
>stiffer.  The more stiff it is, the greater the impedance (the panel's=20
>tendency to resist the transfer of vibrational energy).  The treble end of=
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>the board needs to be stiffer than the bass area.  The relative narrowness=
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>of the board in the treble region combined with more downbearing at that=20
>end produces more stiffness.  The measured bearing can be confusing=20
>because you set the bearing with the board only minimally compressed (or=20
>not compressed at all depending on your technique).  The amount of=20
>measurable beari! ng after the board is strung and loaded will be=20
>different than before it is strung.  You can't really tell after the board=
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>is strung and loaded what the bearing was at the outset.  The tone of the=
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>board will be influenced by the board's response to this downward pressure=
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>and whether it achieves through design and execution the proper impedance=
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>characteristics throughout the scale.
>
>David Love
><mailto:davidlovepianos@earthlink.net>davidlovepianos@earthlink.net
>
>
>----- Original Message -----
>From: <mailto:davidskolnik@optonline.net>David Skolnik
>To: <mailto:pianotech@ptg.org>Pianotech
>Sent: 1/30/2004 3:10:21 AM
>Subject: Re: No downbearing ? REVISITED
>
>Almost one month ago, this a question regarding downbearing was raised:
>
>At 04:09 PM 12/31/2003 +0100, Jean-Jacques Granas wrote:
>
>>I have come across a puzzling suggestion a few weeks ago: Namely, that=20
>>downbearing is not really necessary in order to transfer the vibration of=
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>>the string to the soundboard panel, the mere "grip" that the string has=20
>>on the bridge being sufficient to assure this transfer. Would anyone of=20
>>you with experience in such issues care to comment?
>
>
>Then, At 10:48 AM 12/31/2003 -0500, John Hartman wrote:
>
>>Yes I believe this is correct. Bearing does not directly influence the=20
>>transfer of vibrations. What it does is alter the apparent stiffness of=20
>>the Soundboard and thereby help to control the rate at which the=20
>>vibrations move from the strings into soundboard. Check the archives for=
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>>soundbaord impedance.
>
>Then, At 05:25 PM 12/31/2003 +0100, Isaac sur Noos wrote:
>>I should say that indeed downbearing is not indispensable, but on most=20
>>pianos, front bearing particularly produce a more pleasing (fuller) tone.
>>
>>Bearing being not discernable after the strings have been installed, it=20
>>is often confused with "distance bearing" which indeed is the proof that=
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>>some pressure exist when it is seen, but on some pianos the soundboard=20
>>look flat after the strings have been tense (while down bearing exist=20
>>absorbed by the soundboard) .
>>
>>All depend of the kind of ribbing and construction used (flat ribbing vs.=
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>>crowned ribbing). Most German made pianos are using flat ribs and are=20
>>very sensitive to humidity changes when the soundboard is in good=20
>>condition, so the go out of tune easily in that case. these instruments=20
>>need less down bearing than the ones which are u! sing crowned ribbing=20
>>(B=F6sendorfer for instance).
>>The flat ribbing method "is said" to produce stiffer soundboard assembly,=
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>>while curved ribs need to be pressured more to obtain the necessary=20
>>stiffness. That is what I have understood, very crudely  I confess, from=
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>>the different conversations on those matters.
>
>
>By the second (Isaac sur Noos's) response, what was a potentially=20
>illuminating or controversial discussion, was re-routed to yet another=20
>review of crown and the crowning process.  None of the subsequent=20
>contributions sought to address the original question (in fact or in=20
>spirit), or to clarify John's response.  Here is some of what I felt was=20
>missing:
>
>Jean-Jacques, what was the original source of your 'puzzling=20
>suggestion'?  (previous posting?)  The mere "grip" , as you described=20
>would, presumably, refer to the side bearing of t! he bridge pins.  This=20
>would seem to promote  the theoretical conclusion that the energy is=20
>channeled from string to bridge exclusively by the bridge pins; that the=20
>function of the front  edge of the bridge top may simply be to limit the=20
>downward excursion of the string.  Does it have any role in creating a=20
>reflective terminus of the string? And if so, how much force is required=20
>to prevent  (or control?) energy leakage to rear string segment?  Is it=20
>presumed that  the transfer of energy would be unaffected by the presence=
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>of either positive bearing, no bearing, or, for that matter,  negative=20
>bearing, as long as the bridge pins held onto that string,?
>
>John's response is, I think, unintentionally misleading. He first suggests=
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>that Jean-Jacques's  statement is correct, but then immediately attributes=
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>to downbearing the [important?]ability of controlling "the rate at which=20
>the vibrations move from the strings into s! oundboard". If there is a=20
>point of differentiation to be made here, it seems inordinately subtle,=20
>compared to the resulting impression conveyed that downbearing is not an=20
>essential component in piano design and engineering. Unless that is the=20
>meaning that is intended!?
>
>Finally, before Isaac Sur Noos directed the discussion towards crown, he=20
>made some comments which, if I understand them correctly, are additionally=
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>confused:
>>I should say that indeed downbearing is not indispensable  but on most=20
>>pianos, front bearing particularly produce a more pleasing (fuller) tone.
>
>To summarize then, downbearing isn't essential, unless you want the piano=
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>to sound good.??
>
>With regard to downbearing being discernable, or measurable  (see quote=20
>above)... what IS measurable is, as he puts it, distance, or string=20
>deflection,  I may not be able to tell how much the board has flattened in=
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>response to X amount of original downbearing, but if there is no=20
>measurable deflection, there is no downbearing.  Is this not true?
>
>Thoughts?
>
>
>David Skolnik
>
>

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