This Needs A Definitive Settlement was RE: 12 cents

[Ron Nossaman]

>I too am convinced that the bridge plays a very large part in pitch 
>stability.  Specifically, as you have said Ron, how well the strings 
>render across it. Have there ever been any experiments regarding a 
>laminate of some kind on the bridge top before the pins are drilled?

I don't know, but one thing is pretty clear. The vast majority of 
resistance to a string rendering across a bridge is from the side bearing 
on the pins rather than from the bridge cap. In trying to picture how 
bridge caps are crushed by strings with seasonal expansion, I worked out 
the friction levels between pin and string. At a 10° side bearing angle and 
160# tension, it takes about 14.7# to move the string up and down a 
vertical bridge pin with no downbearing on the bridge. I assume it would 
take a similar amount to slide the string fore and aft on the bridge pin as 
well. That's two sequential friction differential points @ 14#+ each 
between the speaking length and the back scale termination.

A 400mm length of 0.039" wire tuned to 440hz will be at a bit over 168#. At 
437hz, which would be about 12 cents down, it would be at about 166#. You 
are making a 2# change in the speaking length against a 14#+ friction point 
at the bridge. I don't see any mystery at all as to why the string doesn't 
render across the bridge immediately during the tuning to equalize the 
segment tensions. It will render slowly, however, over a couple of days or 
a week as minute dimensional changes from temperature and humidity break 
the friction in small increments and allow the string to creep across - 
messing up the tuning. This is also one of the main reasons why I don't see 
any possible way that a tuned duplex can ever really be in tune with the 
speaking lengths.


>I'm thinking of some sort of brass sheeting or other permanently 
>lubricious material. Further since there is wear on the side of a bridge 
>pin causing a small divot in the surface over which the sting passes it 
>seems that a headless screw might be beneficial here. Perhaps even 
>Stainless steel for it's hardness? If false beats that we all know and 
>love develop we could just turn the pin to a clean surface. Since these 
>are screws and have possibly more contact with the wood than a straight 
>pin they might not get as loose as soon. Thoughts?
>
>Greg Newell

I'd rather see a bridge cap that doesn't change dimension as badly with 
humidity swings, and thus doesn't damage either itself or the pin as badly 
in the first place, or a different termination system altogether. But 
that's a different concern. We still have a high friction point or two 
between the string and the bridge pin(s).

Ron N