Wapin Revisted

[Ric Brekne]

Hi Tim, Cy and John.

Interesting we have already what looks to be 3 different interpretations 
of what is happening to the pulse.  Seems clear to me that the 
reflection would be influenced by the whatever angles are involved in 
the clamp. I did a kind of macro experiment a while back with a rope 
terminated different ways and the effect was pretty clear.  A slanted 
pin caused the pulse to be deflected differently then either a purely 
horizontal or vertical. You could see an initial sideways jerk as the 
pulse repelled from the slanted pin.  Perhaps this causes some degree of 
loss ?

The high speed photography that Dr. Birkett took was quite revealing 
indeed. I only got to look at a couple things he did the first two nites 
of the convention. One seires done with Tim, and another single 
experiement I helped with on a standard configured piano.  Some of the 
thoughts I've been having about what happens to the initial pulse in 
general seemed supported.  For one thing the initial pulse and 
reflections look a bit more like a Gausian wave then a straight 
traveling wave. I didnt get to see a side by side comparison of a wapin 
vs a standard bridge pin... and no doubt one would have to study closely 
for some time to start drawing any conclusions... but Birketts take on 
these kinds of discussions is something I like immensely... namely that 
if you cant measure it or photograph it... then there isnt a lot of 
reason to start making sweeping declarations about how a thing functions. 

Anyways.. back to wapin ...  I am wondering at this point whether or not 
the <<definition>> or focus of the termination at the bridge is what is 
at work here. A clearer focused pulse reflection could result in less 
loss and more returned energy for the string... ? 

It was an interesting afternoon and evening I spent with Tim and Dr. 
Birkett in Rochester thats for sure.  Thanks to the both of them for 
allowing me some hands on time in a bit of what both do.

Cheers
RicB


Tim Coates writes

We initially took video of four strings in four different areas and
marked them for the video "after". Unfortunately, while the exhibit
hall was closed someone took it upon themselves to remove the markers.
Fortunately, they were not able to remove all of the marker from one
of the bass strings. The "after" video was taken in the "Rebuilders
Gallery". It showed exactly what Michael Wathen has been saying
happens from day one: The waves rebound off the bridge with more
intensity. It is very evident beginning with the rebound of the very
first wave. The rebounded waves reinforce the standing wave. A
picture is worth a thousand words.

Tim Coates