Wapin Revisted

[Ric Brekne]

Hi David

    /Ric -

    This was one (just one) of the reasons I was so sad at not being able
    to be in Rochester. I hope Steve Birkett does make the DVD available./

Im sure he will.

    /You said a few things:

     >the initial pulse and reflections look a bit more like a Gausian
     >[sic] wave then a straight traveling wave/

To begin with... it should have been spelled Guassian... and I say this 
only because of an applet I ran into once that struck me as very 
similiar to the wave action I see in Birketts high speed photography.  
The initial pulse  looks sort of like a small upwards facing loop in an 
otherwise straight string. It travels along the wire and hits the bridge 
whereupon the loop reverses polarity.. i.e. faces downwards. But the 
thing is it really doesnt look like the amplitude of the loop ever goes 
below (or perhaps only barely below) the initial string line.  If you 
have a gander at the following page :     
http://www.kettering.edu/~drussell/Demos/reflect/reflect.html , neither 
the absolute soft or hard examples seem to fit... rather something 
inbetween seems to happen.  Of course one would have to examine the high 
speed photography much closer to be sure.. but it appeared convincingly 
enough to me that the reflected pulse highest amplitude did not go below 
the origional string line until the pulse had traveled quite a ways back 
across the string. By the time it got to the agraffee... it was all 
below the string line and the same thing happens again in reverse.  If 
true.. it means that the pulses force on the bridge is in an upward 
direction, and the restoring force downwards never pulls the soundboard 
below its origional height.  Only after the traveling pulse dissipates 
into a standing wave does there appear to be an upwards and downwards 
force on the bridge that is equally above and below the origional string 
line.

    /You also paraphrased Birkett along the lines of  "namely that if you
    can't measure it or photograph it...".  Well, I've been wondering
    about something for quite some time, but haven't known exactly how to
    pursue it, though the information is probably right under my nose,
    (as in previously discussed on this list).  How does wire look (and
    act), molecularly, at rest, and how does that molecular structure and
    behavior change as tension is applied, and as it approaches and
    attains breaking point?  On what level does the behavior of the wire
    change as a response to material imperfections (in fact, how uniform
    is the molecular structure of piano wire?brand to brand?) or to
    physical distortions (bend / crimp) or to the physical process of
    termination?  Did Birkett speak of making any observations along
    these lines?
    /

No... he didnt get into that kind of stuff at all... Tho I suppose the 
jist of what his point was holds just the same.  I'll let him speak for 
himself on the matter tho.  I just understood his point to be that all 
the math models and theories in the world are and never will be 
declarations of truth or fact.  If you can observe something on the 
other hand... well its rather hard to dispute what you can measure... as 
far as that goes. 


    /Lastly, I'm not sure what you mean by:
     >  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.

    Sorry to have missed you on your trip to the states, and I hope the
    cinematic references were not too obscure (or too obvious) for
    you.  Any of you.

    David Skolnik/

I just meant that the exact conditions and angles of the semi clamped 
termination at the bridge in themselves could perhaps influence 
significantly the efficiency of the reflected pulse.  The pulse will hit 
the bridge and some of its energy will be used by the soundboard/bridge 
assembly in making the sound we hear... some of it will be reflected 
back down the string for further use... and some of it will get lost due 
to various things like friction.  Perhaps there is something about the 
angle of initial reflection that touches directly upon how much gets lost ?

Just musing... as usual you see. 

Better ?? :)

btw.. it would have been cool to have bumped into you too !  It was 
great fun meeting so many pianotech folks this time around. No exceptions !

Cheers
RicB

-------------- next part --------------
An HTML attachment was scrubbed...
URL: https://www.moypiano.com/ptg/pianotech.php/attachments/20060814/ea6af0a3/attachment.html