Official Luthiers Forum!

It's common knowledge that increasing brace height is the most effective way to increase stiffness per weight unit. It seems a lot of people have certain guidelines that a bridge plate should be a certain size( like cover the bridge footprint) so the top doesn't belly or roll forward. But are these low flat graphs really necessary other than to keep the strings from eating through the top? Why not increase the height of the bracing around the bridge or even add a thin tall brace behind the plate if more support is needed?

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Jeremy Douglas

No. They do have a structural function but that can be met in other ways, as you suggest.

I will say that, in my experience, everything you do around the bridge has a big impact on tone and it's not necessarily a simple matter of using whatever provides the best stiffness/weight ratio.

If you have a beater or a test body, I'd suggest trying several configurations on that before committing to a radical change on a "real" guitar.

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http://www.chassonguitars.com

That's been done- the so-called PMTE brace...(mass + support)
http://www.proulxguitars.com/buildup/build6.htm

I think another function of the bridge plate is to 'spread out' the forces a bit and prevent a 'stress riser' at the edges of the bridge?
Just a thought...

Cheers
John

Thanks guys, that confirms what I've been thinking.

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Jeremy Douglas

The plate should also help lower the glue stress at the back edge of the bridge, especially if it extends a bit beyond the bridge. When something stiff (bridge) is bonded to something flexible (top), high stresses are found at the edges of the interface (in engineering terms, it's a stress concentration due to a stiffness discontinuity). For example, glue a rubber band to something stiff; pulling it causes it to peel away easily, starting at the edges. In guitars, braces are usually tapered to ~0 at their ends, and bridge plates give a little stepped 'taper' as well. Still, the glue stresses are pretty small compared to glue's typical capacity, so while the plate helps, it's probably not critical.

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David Malicky