Seating strings

[Ric Brekne]

Hi Phil

Nice posts. I appreciate the way you take due caution to relating maths 
modling to real life situations instead of simply spinning off a few 
figures and declaring universal truths. The point you bring up below is 
one (amoung several) that hasnt really been looked at.  It is simply 
assumed that the strings force upwards for even a hard blow is not 
enough to contribute to the string moving upwards on the pin. I dont 
know myself how much of a yank there is there... but it has to be pretty 
signifiacant to get the mass that the soundboard is along with the 
string plane to vibrate in a large enough amplitude to create the volume 
of sound we hear.  I did do a cute little experiement a while back... 
put a penny on the string just at the bridge pin and whack the key.  
Dont get in the way of the penny... :)

Another moment that bothers me which I see no one looking at is the fact 
that the string is forced into an unatural curve across the bridge 
surface to begin with. A string pushed up by a flat surface the width of 
a bridge will not (without bridge pins) lay perfectly flat on that 
surface. It will tend to bend around the surface being highest in the 
middle.  The bridge pins force the string to flatten out, creating 
essentially two fulcrum points where the string contacts the bridge. 
Which forces are doing what in this regard I dont know... but it would 
seem to me that since the string wont be comfortable just laying flat as 
it were. 

A third point which relates to the friction by the pins that seems 
totally over looked is that these also are vibrating in their own 
fashion. For that matter the whole assembly is moving around, components 
phasing in and out .... all in all a pretty complicated picture.

Seems to me that  carefull observation clearly reveals that strings do 
indeed somehow climb up these pins.  Just how remains perhaps a mystery. 

I sure would like to hear more about Maninnos video tho.... :)

Cheers
RicB



Phil Ford writes

There is vibration from play.  I don't know how much variation in the 
forces at the pin it yields.  I would think it would be fairly small even 
for a hard blow.  It might be enough to overcome the frictional forces.  I 
suppose it depends on how close the so-called Parallel force is to the 
Frictional force.  If it's close, then the periodic increase from the 
vibration should be enough to overcome the frictional force and cause the 
string to move.  If the frictional force is significantly higher, because 
of geometry, materials, or surface condition, then the force increase from 
the vibration wouldn't cause the string to move. I don't know what you mean 
by movement from thermal effects.