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Old 12-29-2011, 09:32 AM
Robert J Spear Robert J Spear is offline
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Join Date: 07-12-2011
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Default string tension

It was quite a pleasure to return to this thread and find some activity on the fifths-tuning topic. Since I've just designed and built (or am building) a couple of new basses, including one five-stringer, the question of string tension is one that couldn't be avoided. What I learned is that string tension and tension on the top of the instrument are not the same thing. The tension of the strings is controlled by a lot of factors including diameter, materials, tuning pitch, and length, but tension on the belly is a function of the string angle over the bridge.

Consider if you had a bridge carrying strings at an angle of zero. There would be no downward tension to speak of on the belly except the bare minimum amount needed to keep the bridge in place. It wouldn't matter how many strings were on the bridge; pressure on the belly would always be zero. When you begin increasing the angle, only then does pressure on the top become a factor. If you add strings, the downward pressure increases; if you remove strings, it decreases. I've read many comments in the literature that indicate that the reason many old basses only had three strings was that it allowed a freer top vibration and produced less pressure.

Downward pressure on the top can be mitigated by decreasing the angle of the neck or by raising the saddle. I used a combination of the two, but it's a game that can only be played so far. It was a very interesting exercise. A couple of years ago I had the chance to hear a highly experimental 15" viola a friend of mine made that had almost no string angle at the bridge. When it came out of its case, my immediate reaction was that it was an ingenious design that would have absolutely no sound at all. I was amazed at how good it sounded! Lots of mysterious things to learn in this biz.
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