>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
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