tapping strings

[David Skolnik]

---------------------- multipart/alternative attachment
At 03:56 PM 04/08/2002 +0200, you Richard B wrote:

>(This part by Richard B )
> > Downbearing as I view it has to be measured that way.  You already
> > know the tensions involved... you need to know the angles you are
> > subjecting the wires under these tensions to. If you measure an
> > instrument that is already strung and up to tension...then you need to
> > know how much the panel has been pressed down as well to really know
> > what the actual downbearing is.  Knowing both is valuable anyways I
> > might add.
>(This is by David Skolnik)
> > Just so that I'm clear, are you saying that it is not possible to take
> > measurements with a gauge (and string under the 'panel') and make some
> > conclusion about the downbearing present in the piano?
>(Richard B again)
>Hmm...... stricktly speaking the string and gauge under the panel gives
>you information as to whether or not there is crown.... and nothing
>more.

Richard, I think you misread my post.  I said "gauge (and string under the 
'panel')", meaning a gauge of some sort on top and the string underneath.

>Ok... add to the picture that you can confirm positve bearing from strings 
>with a
>rocker gauge or something like that...

While all bearing gauges have the potential to be deceived, I believe the 
rocker type is inadequate to the task of accurately reading the 
configuration of the string deflection.  A bubble gauge, when properly 
used, is much more revealing.

>  you still dont know how much downbearing there is... because you cant 
> know how much the soundboard is resisting whatever downward pressure 
> there is.. so you cant figure it
>out whatever angles you measure.  You can do that however when you know
>what the upward pressure is... and of course when its zero.... that makes 
>things easy.

Ron N's clarification is worth repeating here

>String downbearing is the product of tension and bearing angles. The board
>is, under all circumstances, exactly resisting the string downbearing force
>- exactly. The measured crown of the board, compared to the downbearing
>angles, is an indication of how successfully the board is resisting the
>string downbearing force.

I think it may have been Bob Hohf who used the term 'residual downbearing", 
to, as I understood it, refer to the measurable deflection after the string 
has compressed the board as much as it was going to.  On a healthy (ie. 
crowned board), that 'residual' downbearing could theoretically be anything 
from zero + .0001 (?) and up. But if it were zero, you have none, and if 
you show a negative  deflection, you enter a different world of 
forces.  From the point of view of measuring this deflection when there is 
not much to be seen, how accurately can it be measured?  Again, in a strung 
piano, is a test string, run next to, or even in the place of, an existing 
string, going to be able to account for the effects of cap 
indentation?  The problem is a bit quantum...in order to truly duplicate 
the piano string with the test string you must recreate the offset created 
by the bridge pins, and yet, as soon as you do, you are potentially 
distorting the vertical direction  of the test string travel.

Another part of the problem we are confronting in this discussion is that 
when we speak of 'Downbearing', our focus wanders between soundboard 
loading,  string termination or  bridge loading (energy from string to 
bridge).  We've been taking an extended vacation from the last point 
(Behavior of Soundboards, etc) and the issue of loading is more in the 
realm of rebuilding (calculating the force relationship between downbearing 
and crown), but string termination, for whatever its contribution to the 
total, is all about angles, and is something we need to be able to measure 
accurately.

So, are all the methods of measuring termination angles equally accurate?


David Skolnik
---------------------- multipart/alternative attachment
An HTML attachment was scrubbed...
URL: https://www.moypiano.com/ptg/caut.php/attachments/0c/5b/21/9c/attachment.htm

---------------------- multipart/alternative attachment--