Brian Trout wrote: > I was wondering, If you need to undercut a bridge, is it acceptable to > undercut in more than one direction? > > Here's what I'm thinking... > > Lets say we have a bass bridge that has a footprint of 12"L x 1.5"W (x 2"H). > If I needed to undercut that bridge, would I be making the footprint > something like 12" x 7/8" ? Is that the direction you would undercut? No. I can't think of any reason why you would want to make the footprint narrower. The bass bridge has enough trouble with stability the way it is and I can't think of any acoustical or structural benefit to this. Your reasoning, please... What would be the point and am I missing something? > And the other part was, is it ever a good idea to undercut away from the lower > > end of the bridge so that the footprint would be more like 10.5" x 7/8" (still > flush to the end on the tenor side)? This is the way it is done -- see Ron's little ascii sketch. (Well, the footprint would be something more like 10.5" x 1.5" with the cut-away being only on the bass end. The tenor end being flush.) Typically the bass bridge is cut back to the point where it crosses over the first rib. (It helps if you are also designing the rib set so that you can coordinate these two points.) The idea is to more or less duplicate the function of the cantilever -- that is, to keep the bridge from restricting the soundboard's motion. But without introducing the drawbacks of the actual cantilever. > I'm trying to get a feel of how far you take this. Is it of any advantage > to make the bass bridge in such a fashion as to put it on several "stilts" > leaving sections underneath open? Not that I am aware of. This has been done -- indeed, is being done on certain Steinway tenor bridges. It doesn't have any effect there either. > That would really let the soundboard move?, Only if you expect the soundboard to move on its own. They don't, generally. They are driven by energy coupled from the string through the bridge. > but then I'd be worried about a good sound energy transfer... Yes. Although, on reflection, there probably wouldn't be much energy loss as long as the "feet" ended up on the rib centerlines. So this might be one of those "features" that, while not doing any good, at least wouldn't be doing any harm. That's better than some other highly touted "features" currently in vogue. Del
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