Hybrid bass building; back thickness?

[MPU]

I just got the GAL plans. I ordered 5-ply 2mm aircraft grade plywood for ribs. For back I can choose between 3-ply 4mm or 5-ply 6mm baltic birch. Which way should I go? To me 6mm looks very, very strong and 4mm maybe a biit too thin for this purpose.
As for top I'm going to use pine or spruce, whichever is easier to find.
Marko

[arnoldschnitzer]

Go with the 6mm and keep the bracing light.

[MPU]

Thanks. I was also thinking that thinner back needs thicker braces and vice versa. If thicker back with thinner bracing is the way to go then that's it. 4mm is a bit flimsy as it's only 3 ply. The 5-ply 6mm is way more stiffer.
Marko

[George700DL]

Originally Posted by MPU

Thanks. I was also thinking that thinner back needs thicker braces and vice versa. If thicker back with thinner bracing is the way to go then that's it. 4mm is a bit flimsy as it's only 3 ply. The 5-ply 6mm is way more stiffer.
Marko

I used a ~5.2mm lauan plywood - about the cheapest around here. The GAL plans call for only 4 horizontal braces, with the soundpost supporting one being wide and flat. I followed those plans, only to find out that after the glue dried, the plate curved up (rather significantly). So I went back and retrofitted a single vertical brace in the middle. At the end, I shaved everything down as much as I thought was appropriate. I bet that I could still go back and remove more wood, but so far I'm happy with the sound so I'm leaving it alone.

What surprised me was that the final weight of everything (strung up) is only 21.6 lbs. I thought for sure that I'd have overengineered everything as usual. But I guess there isn't that much wood on it afterall.

George