French Bass full restoration

[Nathan Parker]

Out of ignorant curiosity, what does vibrating the top with sand in it tell you? You have my interest very piqued, and I really appreciate all the pictures and updates in this thread. I love seeing all the details and effort that go into this. Kudos.

[Matthew Tucker]

it just tells me the frequency of the resonant modes of that top. Combined with the weight, it can give a numerical value for stiffness. Sometimes it can reveal asymmetries in stiffness. But it tells me no more about the tone of the bass than other measurements such as the width of the plates. For the moment it is just another measurement to keep track of and compare with other basses, but its fun to do and looks cool.

[Nathan Parker]

It does look cool, that is for sure. So, ideally, would all the sand be symmetrical? I see that it mostly is, except at one frequency were there is a slight variance. It is pretty incredible the different patterns it forms based on frequency of vibration. How consistent are the results? If you were to do the same test back to back, are the results identical?

Sorry for all the questions, just very curious.

[Matthew Tucker]

yes same tests back to back are identical if nothing else changes. I suppose if you take the view that symmetrical plates are ideal or necessary (although there's no evidence that this is the case) then symmetrical shapes would indicate this.

My ideal is to get the tea-leaf patterns looking as much like Yosemite Sam as possible. Yosemite Sam is the holy grail of chladni enthusiasts ... I have a long way to go.

[Ken Smith]

Originally Posted by Matthew Tucker

yes same tests back to back are identical if nothing else changes. I suppose if you take the view that symmetrical plates are ideal or necessary (although there's no evidence that this is the case) then symmetrical shapes would indicate this.

My ideal is to get the tea-leaf patterns looking as much like Yosemite Sam as possible. Yosemite Sam is the holy grail of chladni enthusiasts ... I have a long way to go.

If you get what you call Yosemite Sam, what does that mean? Is this something a maker shoots for or an accident hoping to happen?

Doesn't that top need some cleats for all the cracks you glued up so far? How will Sam react to that?

Have fun..

[Matthew Tucker]

Yosemite Sam is just me being silly, Ken. For me it is JUST another measure of the top and doesn't really give any more clues about what must be done than does the distance between the FFs or the size of the endpin block or the width of the lower bout. Since I have the bass top off I can make these measurements and see what happens when i remove wood where I think it needs to be removed. I'll also be able to compare what happens when I cleat the cracks, and when I add the new bass bar.

The patterns are cool but are only a flag to show that the particular resonance mode has been met. I don't know enough about the shape to be able to draw any conclusions. And there are too many variables ... such as the arching shape for starters. The most interesting number I think is the frequency of vibration which combined with the weight of the plate is a measure of stiffness. If, after I do everything and re-cleat and replace the bass bar, the modes appear at the same frequencies, I can - I think - assume that the plate is fairly consistent with how it started out. If on the other hand, the frequencies are lower, but the weight is the same, this will show me that what I have done has increased the flexibility of the plate. I can make those sorts of observations.

I could - and will - also flex the plates with my fingers, tap them etc - and you DO get a lot of tactile feedback when you are working on the plates with the planes and scrapers. But this is more subjective.

Nothing here, unfortunately, will tell me whether I've done enough ... or gone too far!

See where I'm coming from? I'm not looking for a magic pill; it would be nice in a way if we could ****yse this work scientifically but I don't think this is at all easy - at the end of the day a luthier's work a series of educated hunches and generalisations. Some people might think that this sort of mucking around is a waste of time but for me, the more information I have to inform my instincts, the better.

[Thomas Erickson]

I wonder if there is a comparable system for testing resonance of a plate on a complete instrument. Seems like testing the plate on its own, then as part of the complete assembly, and finally under tension would give a lot of insight that could be applied not only that instrument but to making new ones and improving older ones.

[Craig Regan]

So... Is the plan to re graduate, then put the bass bar and cleats back in? Or is it a combination of installing and graduating as you go?

Also... how do you keep from losing your crack locations?