Official Luthiers Forum!

BTW.......I just re-read my post above. I hope it didn't come across like I was questioning Al's opinion as I respect respect Al's opinion very much and have learned so much from his posts. However, Al's statement caught me by surprise after reading Siminoff's book and reading how he tested his bridge vibration theories. I now realize you should take very little information as accepted absolutes.

I am curious to hear opinions about placing the stiffest brace on the guitar, the bridge, in the middle of the lower bout........then placing 150lbs of tension (or more) on that bridge. Seems this would tend to kill vibration in the spot you want moving most.

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Formerly known as Adaboy.......

Daryl Young wrote:
"I am curious to hear opinions about placing the stiffest brace on the guitar, the bridge, in the middle of the lower bout........then placing 150lbs of tension (or more) on that bridge. Seems this would tend to kill vibration in the spot you want moving most."

I'm sure you'll get lots of opnions. I'd love to get some data!

From the testing I've done it seems to me as though tensioning the strings does not effect the shapes or frequencies of the lower-order top modes, the ones you can see with Chladni patterns, at least, not on flat tops or classicals. At the time I did these experiments I didn't have a good way of looking at the damping of these modes, or finding out whether there was a difference in mobility, so, as usual, I need to go back and re-do them.

Another issue is that these low-order modes aren't the be-all of guitar sound. In fact, it can be argued that the stuff you can't see very easily is far more important. Some of that stuff is getting easier to get at, using laser holography, for example, but that's expensive technology for a working luthier.

In terms of the effect of the mass and stiffness of the bridge on top vibration, I guess I could say two things. First: we're pretty well stuck with it, at least if what we want to make are 'traditional' designs. Second: I'm not sure it's all that bad. The few instruments I've heard that had lightly built tops and some arangement to take the torque off the bridge didn't sound very good to me. Usually they're bassy, and even tubby: not nearly stiff enough to get the trebles to work well. I have to point out that I have not heard _every_ such design, and I'm sure there are some that work better.

It's interesting to note that the guitar is one of the most efficient instruments, in terms of turning input energy into sound. It may be hard to believe, but guitars seem to be about twice as efficient as violins, for example. Generations of luthiers have worried these designs into yeilding some pretty impressive performance. This is not to say there is no room for improvements, particularly through the use of stuff like carbon fiber that C.F. Martin I never heard of. But let's not knock the traditional designs until we've made some serious improvements.