Quoting Ron Nossaman <rnossaman@cox.net>: > > >I wonder what > >basis there is for our notion that bridge tops should ideally be > flat. > > Fred, > From a practical engineering standpoint, the flat top is a balance > or > compromise between termination quality and durability. Presuming > positive > front bearing (angle between bridge top and speaking length), it > gives a > more defined and positive termination point at the edge than a top > that is > curved to be tangent to the string plane, while being less easily > crushable > (and cheaper to build) than a top that is grooved or "V'd" down the > center. > Yes, from a practical standpoint, one wouldn't design curve into the top of a wooden bridge (with a material that wouldn't crush/deform, though, the question might be theoretically pertinent). The real thrust of my musing was to consider "going with the flow" in real world situations, where recapping or bridge replacement aren't going to happen (at the particular moment). "Curvature happens." Bridge tops crush at both sides more than on top. This is what we find most often in the field. If I want to clean up terminations (again, short of recap), I'm thinking it might make practical sense to leave a tad bit of that curvature - with the proviso that there be positive front termination as demonstrated by running a string from capo and verifying that the front edge of the notch is touched first. I'm thinking this may be a more stable "fix" than making sure the cap is flat: that bit of curve might impede future grooving by supporting the string. Oops! Reading what I just read revealed the fallacy of my thinking. If humidity swing is the major cause of grooving (and I have been persuaded by Ron's arguments and my own thinking and observing that this is the case), having "the middle support the string" would have next to no effect. Meaning that one would simply be closer to having bad termination - less crushing would lead to negative front bearing - with a curved profile. Oh, well, shows that one should think through a bit more completely before spouting. BTW, one example of my own observation that might be of interest: A Steinway A from the 20's, all original, spent the first 60 years of its life in a stuffy apartment in San Francisco (which has milder humidity swings than most parts of the country), then came to Albuquerque where it was immediately humidity controlled. Never had any string tapping that I know of. I restrung it a couple years ago, and found absolutely minimal string grooving on the bridge tops, and next to no curvature. And bridge pins with very minor to undetectible grooving. Pins were tight, too. I just restrung it, with no bridge work whatsoever - something I almost never do. I look at this piano as strong evidence that it's humidity swings and tapping that create the grooves. (And this piano has great carry and sustain, and had it prior to restring). BTW, if anyone reading really believes that light tapping doesn't crush bridge tops, take a piece of wire, lay it on a bit of exposed bridge top (above C8, eg) and give it a tap with your brass rod. Even with your hammer shank. Give the amount of tap that has "given focus to the tone," "allowed you to see the string drop," "dropped pitch 4 cents," whatever. Then look at that bridge top. I guarantee you'll see a little groove where none was before. And for those who believe a string "rides up a bridge pin" due to hard playing, try pulling a string up a bridge pin with a stringing hook. I have. I found that I could change the string level in front of the bridge, but determined it was only due to string deformation. Could not get the string to ride up the pin (as measured, eg, by string level on the bridge itself). I'm not saying hard playing doesn't exacerbate the lack of clear termination caused by loss of front bearing (usually associated with heavy grooving). But I have found repeatedly that in cases like this I can "mask the symptoms" (as Ron correctly puts it) just as well by massaging the string toward the pin/notch crotch as by tapping. And massaging won't exacerbate the problem by creating additional grooving. Regards, Fred Sturm University of New Mexico
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