Steingraeber factory pictures, bridge agraffes & adjustable vertical hitchpins

[Ron Nossaman]

>> Someone mentioned something about a presumed vertical vibrational mode 
>> enhancement being automatically something that would simply pump more 
>> string energy directly into the soundboard and actually decreasing 
>> sustain.  I would say that was rather premature stated.... tho I would 
>> be delighted to see any science that backs that idea up.
> 
> Bizarre.  This seems so obvious to me :  the board is driven by the 
> string (via the bridge).  If the string vibrates in a mode that is 
> normal (perpendicular) to the board, then all of its energy contributes 
> to make the board vibrate in a way that will in the end favor the 
> acoustic pressure wave that we hear.  If the string (partly)  vibrates 
> in a plane that is parallel to the board surface, that energy will 
> result in bridge twisting and board compressions that will transfer only 
> a tiny bit of energy into acoustic pressure wave that we can hear.  

Correct, all of which more or less agrees with Gabriel 
Weinreich in the much quoted and revered Five Lectures.


>Now, 
> in the case that the string vibrates in the vertical plane, thus, I 
> think, transferring it's energy efficiently to the board, this doesn't 
> always mean (or am I wrong) that the sustain would dininish, like in the 
> case that the impedance of the board is too close to the impedance of 
> the string.  In this case, impedances respectively are the same, it is 
> just the vector of the forces acting that is more close to the shape 
> that maximizes the transfer of energy (vertical in this case).
> 
> Best regards.
> 
> Stéphane Collin

In the case of the bridge agraffes, it is the increased mass 
of the agraffe that raises the soundboard assembly impedance, 
lowers the resonant frequency, and keeps the sustain up. If 
you could get a string to stay in vertical excursion mode 
without adding the mass of the agraffe, you would increase 
loudness and decrease sustain.
  Ron N