tapping strings

[Richard Brekne]

David Skolnik wrote:

> At 05:05 PM 04/06/2002 +0200, you, RicB, wrote:
>
> >That said there are many who insist that the string must terminate exactly
> >at the same spot on the bridge pin as on the bridge itself.
>
> What percentage of energy is carried by pin, as opposed to wood of
> bridge?  Do they process different vibrational modes?  What is the effect
> of nonsynchronos terminations (wood before pin/ pin before wood)?  What
> other theories are currently active?
>

When you start asking all the "experts" around.... and I mean people who for
all practical purposes have enough experience and education that you simply
have to respect their thoughts and meanings... you are left with the reality
that there is a lot of disagreement out there about all these questions. So in
the end, no matter how brilliant you end up being yourself you have to make
your own call on these things. Look at what you see out there... seems to me
that good old fashioned observation is an under exploited tool in all this.
Take Dales recent post on the Knabe question for example... strings terminating
off the pins alone (as I read that reply) can function.  Non synchronous
termination.... really the case can be made that the truly synchronous
termination simply does not exist to begin with.... if you take that view then
what are you left looking at....?  I would tend to think the answer to that is
"what kind of non synchronous configuration yields the acoustic result you are
after"

> >It has been stated that a convex surface, though it would tend to even the
> >pressure
> >relationships between the bridge surface and strings, would result in a
> >loss of
> >energy.
>
> Ric -can you supply a source of this theory?  Why would energy loss occur?

Well, most recently Ron N's reply to a post I wrote just the other day... and
it has some merit to be sure. Let me try to explain as best my understanding
allows..... Again... the string is not absolutely  terminated to begin with...
energy seeps through to the other side of the termination point. And what so
??  Take an extreme example for illustration. What if you had a "bridge pin" 5
mm out from the notch ? Do you think that as much energy would zip down the pin
into the bridge compared to if the bridge pin was in the same place as where
the string contacts the wood ? What about the energy that goes beyond  the pin
here ? Some of that would have to eventually hit the bridge itself and get
transferred... and some more would have to go into losses for that short length
between. The Convex bridge surface question is really sort of a variation of
the same thing. The string on a flat faced bridge is supposed to bend (if you
will) over the edge and is trapped there by the bridge pin at the same
place...the idea being to provide as total a termination as is possible at that
exact point. The termination is a two component thing.. with one component (the
bridge pin) at very roughly 90 degrees from the other component (the bridge
itself) If you make the bridge convex then you more or less increase the length
of the woods component to the termination..... it takes a wider surface on the
part of the bridge to terminate the same amount of energy.... with accompanying
losses within the string for that little extra wideness.  Now whether this is a
bad thing or not is not for me to say... I would point out though that one of
Wapins claims is that the flat faced bridge with the angled pinning we most
often see yields unnecessarily strong string to bridge coupling, which he sees
as a downside relating to sustain.

> >But then if the flat surface so easily deteriorates as also claimed, (and
> >in a fashion resembling to the convex shape mind you) then perhaps to
> >start with a convex shape might be more useful then presently assumed
> >after all.
>
> I would say in more than just "a fashion"  But in any case, can you explain
> to me how you would measure downbearing on a convex bridge surface?

I would too...  Seems to me that the grooves in the bridge that naturally occur
resemble more a "convexing" of the surface of the bridge (seen from the strings
perspective) then they do anything else.  Incorrect string seating procedures
can of course alter that picture.  Measuring down bearing ?? Hmm.... I suppose
much like I do otherwise.

----------------

To the question of filling the grooves...

> What would you fill them with that wouldn't re compress, or disintegrate?
> If there is such a material, why not use it for the original cap. as
> Richard West mentioned?

I really don't know.... just have played with the idea as I said. I suppose
really the problem might be more one of getting the fill to stay put then
anything else.  Probably not really feasible... but its fun to think about
things.

>
>
> David Skolnik




--
Richard Brekne
RPT, N.P.T.F.
Bergen, Norway
mailto:rbrekne@broadpark.no
http://home.broadpark.no/~rbrekne/ricmain.html