longitudinal mode vibrations

[Paul S. Larudee]

Ron Nossaman wrote:
> 
> >List,
> >
> >What is the relationship, if any, between string torque and longitudinal
> >mode vibrations?
> 
> Hi Paul,
> 
> * I don't believe you got any bites on this one, and I think that's because
> nobody has established any such relationship.
> 
> >When there is torque in the string, I presume there is
> >torsional movement, and my guess is that it would be longitudinal.
> 
> * I'm not sure what you mean here... 
> 
>  Ron

Ron,

Let me amplify my question a bit.  Let's forget wound strings for a
moment.  I have always heard, and it agrees with my experience, that
torque can be a cause of false beats, especially in the upper treble. 
For this reason, we try to avoid putting torque in the plain strings,
and some manufacturers such as Yamaha go to great lengths in this
regard.

Why?  My guess - and it's only a guess - is that when there is torque in
the string and the string is in motion, the torque will not remain
evenly distributed along the length of the string.  When energy is is
added to the bearing point, where the torque stops, it will momentarily
increase the torque, causing the string to roll slightly on the bearing,
and then roll back as tension is equalized again.  This will cause a
torque wave to travel from the bearing point down the string to the
opposite bearing point - i.e. a longitudinal torque wave.  My question
is, How does this affect other longitudinal mode vibrations, or other
string dynamics, for that matter?

In the case of wound strings, the torque vibrations would be partly
(hopefully almost entirely) dissipated by the mass of the windings, but
I am not a fan of putting torque in them anyway.

Paul S. Larudee, RPT
Richmond, CA