Bridge Seating / food for thought -- a retraction

[Porritt, David]

Ric:

You mentioned Jim Ellis' article in the September 1982 Journal and offer
to send it to people if you can get permission.  Anyone can have a copy
of that article if they purchase the 20 year Journal CD-rom which is
available at
https://www.ptg.org/store/product_info.php?cPath=22&products_id=44

dave

David M. Porritt
dporritt at smu.edu

-----Original Message-----
From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On
Behalf Of Ric Brekne
Sent: Wednesday, September 13, 2006 4:47 AM
To: pianotech at ptg.org
Subject: Bridge Seating / food for thought -- a retraction

    Cy Shuster wrote:

     > Isn't it possible that when the string touches the pin above the
    bridge
     > its leverage makes for a less-secure termination, effectively
    increasing
     > the speaking length?

    Which is exactly what I've been saying repeatedly for, what,
    seven or eight years now? Since it's been published now by
    someone official, I suppose it might finally be taken seriously.
    Ron N

Hi Folks.

A few days back I responded to this by stating that this was not what 
had been forwarded here on pianotech in the past. That  was  perhaps a 
rather presumptious statement on my part which I would like to retract.

My understanding of what had been said and explained was definitely at 
odds with the above. But my understanding of someones words do not 
necessarily represent what the respondent actually meant.

I've had quite a bit of off list discussion going on about all this 
loose pin / recessed bridge theory for a good while now.  My own 
perspectives has led me towards thinking along lines that the bridge 
termination as a whole being springy or massy is the determinant for 
whether false beats occur or not. I believe there are solid physics 
grounds for this.  That said,  these same discussions and the last 
exchange on pianotech has directed me to re-read many of Ron Nossamans 
postings on the subject and I believe at this point he is saying 
something very much along the same lines. That a recessed notch edge and

loose bridge pin /contribute/ to the bridge termination becoming more 
springy then massy for the affected string  I do not question.  If that 
is what he (Ron N) has been trying to say then I agree, as far as that 
goes.

Whether a loose pin and a recessed notch are in themselves enough to 
cause this anisotropy to the degree needed to enable a false beat 
remains perhaps in dispute. Its a very complicated picture to begin with

and as I have said before... I can not find a statistical correlation 
between the two. This has led me to believe that there is more at work 
here. It also seems apparent to me that if a termination becomes a 
springy support...then it is not really a termination any longer. The 
"effective" point of termination would correspond very closely to the 
length of string necessary to cause the frequency difference for the 
applied tension. The fact that the pin is moving in phase with a string 
in a given vibrational direction then is evidence that it no longer is 
capable of fully terminating the string.  Perhaps more correct would be 
to say it becomes effectively part of the lengthened string. It should 
also be noted that the amount of side movement needed for the pin to 
move in this scenario is  the same (for all practical purposes) as the 
amplitude of the string vibration at that point for the *lengthened* 
string direction. This puts it in the microscopic range I believe and 
also relieves my concerns about what appeared to be claims of very large

movements (wobble) on the part of the pin. 

I would like to point all interested to the September issue 1982 of the 
Journal.  Jim Ellis has an article series there and has a particularly 
easy to understand analogy with a pendulum experiment that shows clearly

the basic functioning of a springy vs massy support.  Using the pendulum

analogy.. if the support for the pendulum is springy, the pendulum will 
act as if it was longer then it actually is.  The support itself 
<<swings>> in phase with the pendulum. As such it is no longer strictly 
speaking the fulcrum for the pendulum. That is moved up above the 
support and doesn't actually physically exist.   If the supports are 
braced to prevent them from moving <<in concert>> so to speak with the 
pendulum, then the pendulums frequency will increase and its *effective*

length shorten.  The analogy to the piano string is obvious. There are 
several examples which show what happens with 2 and 3 pendulums 
(strings) attached and what happens when mass is coupled to the 
supports.  Reading of this should make clear the mechanism at work  that

can cause a false beat if anisotropic localized boundary conditions at 
the bridge exist for any given string in significant enough degree.  
That is to say if the string sees the bridge as more springy (to large 
enough degree) in one vibrational direction then in another.

Otherwise I would like to state unequivocally that I share the 
skepticism of many on this list towards aggressive string seating.  I 
stand by my position that string seating is a necessary procedure to 
carry out, but only when a string (for whatever reasons) finds itself 
unseated in the face of a bridge whose entire surface is at or above the

line of deflection for the string. Whether that can happen or not is 
another discussion entirely. I personally see no reason to doubt that it

can.

If anyone lacks the aforementioned article.. I will see if I can get it 
to you. I will of course have to ask permissions.  Just email me off
list.

With hopes this can bring the subject matter further.

RicB