No downbearing ? REVISITED

[David Love]

Please don't hold it against me for too long :-).

As to part one of your question, I think the answer is that "after"
measurements simply don't tell the whole story.  When destringing a piano
it would be wise to measure the bearing (and crown) before and after to
determine how much the board compressed.  The information shouldn't be
dismissed, but one should be cautious about drawing any conclusions knowing
only half the story.  

As to part two, I think there are several regular contributors to the list
(Del Fandrich, John Hartman, Ron Nossaman, Ron Overs and others) who are
better equipped to answer that question than I am and hopefully they will
chime in.  One thing you might consider, however, is anecdotal evidence. 
Boards with negative bearing don't necessarily exhibit coupling problems. 
Were positive bearing necessary to avoid coupling problems, you would
expect to see these problems on all pianos that have negative bearing. 
That's just not the case.

 David Love
 davidlovepianos@earthlink.net


> ----- Original Message ----- 
> From: David Skolnik 
> To: davidlovepianos@earthlink.net;Pianotech
> Sent: 1/30/2004 8:44:34 AM 
> Subject: Re: No downbearing ? REVISITED
>
>
> David Love -
> Thanks for responding.  I haven't forgotten that you started all this
with your Negative Bearing question a few years ago.  Let's see if I can
keep this on track long enough for me to understand.  To simplify things a
bit, can we agree to acknowledge, then ignore the fact that we cannot
determine the original bearing set up from measuring the strung piano? Why
does there appear to be this growing consensus that these "after stringing"
measurements are deceptive, confusing, and of no value?  Whether or not the
board is being compressed  (i.e. stiffened) by one area of the string
scale, if I get readings showing zero or negative downbearing in a section
of the piano, is it to be dismissed because there is downbearing SOMEWHERE
on the board? 
>
> With regard to transfer of vibrations, can you, David, or anyone else,
direct me to recent discussion that supports this view of the irrelevance
of downbearing in this process?  (I will scan the past years posts if you
cannot.)  If such is, in fact, the case, and if you could create the
hypothetical soundboard with sufficient stiffness WITHOUT employing
downbearing's compressive function, is there, in your opinion, ANY aspect
of the mechanical transfer of energy from string to bridge ( & board) via
bridge pin, that would suffer in the absence of such downbearing?   For
example, if the string were to traverse the bridge, captured by the pins
(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
string impulse)  What is the implication regarding the way the string
energy transfers from string to bridge to board?  Did I miss the resolution
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
the bridge, not due to any downward pressure of the strings onto the
bridge.  That coupling is achieved by the interlocking of the string
through the bridge pins .  Whether or not you have downbearing will not
influence this coupling.  The downbearing effects the amount of downward
pressure on the soundboard.  When the board is compressed it gets stiffer. 
The more stiff it is, the greater the impedance (the panel's tendency to
resist the transfer of vibrational energy).  The treble end of the board
needs to be stiffer than the bass area.  The relative narrowness of the
board in the treble region combined with more downbearing at that end
produces more stiffness.  The measured bearing can be confusing because you
set the bearing with the board only minimally compressed (or not compressed
at all depending on your technique).  The amount of measurable beari! ng
after the board is strung and loaded will be different than before it is
strung.  You can't really tell after the board is strung and loaded what
the bearing was at the outset.  The tone of the board will be influenced by
the board's response to this downward pressure and whether it achieves
through design and execution the proper impedance characteristics
throughout the scale.  
>  
> David Love
> davidlovepianos@earthlink.net
>  
>  
>
> ----- Original Message ----- 
>
> From: David Skolnik 
>
> To: 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
downbearing is not really necessary in order to transfer the vibration of
the string to the soundboard panel, the mere "grip" that the string has on
the bridge being sufficient to assure this transfer. Would anyone of 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
transfer of vibrations. What it does is alter the apparent stiffness of the
Soundboard and thereby help to control the rate at which the vibrations
move from the strings into soundboard. Check the archives for 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
pianos, front bearing particularly produce a more pleasing (fuller) tone.
>
>
>
> Bearing being not discernable after the strings have been installed, it
is often confused with "distance bearing" which indeed is the proof that
some pressure exist when it is seen, but on some pianos the soundboard look
flat after the strings have been tense (while down bearing exist absorbed
by the soundboard) . 
>
>
>
> All depend of the kind of ribbing and construction used (flat ribbing vs.
crowned ribbing). Most German made pianos are using flat ribs and are very
sensitive to humidity changes when the soundboard is in good condition, so
the go out of tune easily in that case. these instruments need less down
bearing than the ones which are u! sing crowned ribbing (Bösendorfer for
instance).
>
> The flat ribbing method "is said" to produce stiffer soundboard assembly,
while curved ribs need to be pressured more to obtain the necessary
stiffness. That is what I have understood, very crudely  I confess, from
the different conversations on those matters.
>
>
>
> By the second (Isaac sur Noos's) response, what was a potentially
illuminating or controversial discussion, was re-routed to yet another
review of crown and the crowning process.  None of the subsequent
contributions sought to address the original question (in fact or in
spirit), or to clarify John's response.  Here is some of what I felt was
missing:
>
>
> Jean-Jacques, what was the original source of your 'puzzling suggestion'?
(previous posting?)  The mere "grip" , as you described would, presumably,
refer to the side bearing of t! he bridge pins.  This would seem to promote
the theoretical conclusion that the energy is channeled from string to
bridge exclusively by the bridge pins; that the function of the front  edge
of the bridge top may simply be to limit the downward excursion of the
string.  Does it have any role in creating a reflective terminus of the
string? And if so, how much force is required to prevent  (or control?)
energy leakage to rear string segment?  Is it presumed that  the transfer
of energy would be unaffected by the presence of either positive bearing,
no bearing, or, for that matter,  negative bearing, as long as the bridge
pins held onto that string,?
>
>
> John's response is, I think, unintentionally misleading. He first
suggests that Jean-Jacques's  statement is correct, but then immediately
attributes to downbearing the [important?]ability of controlling "the rate
at which the vibrations move from the strings into s! oundboard". If there
is a point of differentiation to be made here, it seems inordinately
subtle, compared to the resulting impression conveyed that downbearing is
not an essential component in piano design and engineering. Unless that is
the meaning that is intended!?
>
>
> Finally, before Isaac Sur Noos directed the discussion towards crown, he
made some comments which, if I understand them correctly, are additionally
confused:
>
> I should say that indeed downbearing is not indispensable  but on most
pianos, front bearing particularly produce a more pleasing (fuller) tone.
>
>
> To summarize then, downbearing isn't essential, unless you want the piano
to sound good.??
>
>
> With regard to downbearing being discernable, or measurable  (see quote
above)... what IS measurable is, as he puts it, distance, or string
deflection,  I may not be able to tell how much the board has flattened in
response to X amount of original downbearing, but if there is no measurable
deflection, there is no downbearing.  Is this not true?
>
>
> Thoughts?
>
>
>
> David Skolnik