top bracing for alternate woods

[hat]

When using alternate top woods ,such as Redwood or Cedar, are there basic starting points to use in adjusting the size ( stiffness) of the top braces to accommodate the differences in wood strength from Spruce?

[Alan Carruth]

The best way to go about it is to adjust the top thickness to get the same stiffness in bending along the grain. Then you just use your regular bracing. For softwoods the Young's modulus along the grain, which predicts the stiffness at a given thickness, pretty well tracks the density, so a simple density calculation is a decent proxy if you don't want to actually measure the stiffness. Although different species will have different average density, they all vary a lot, and there's plenty of overlap. As an example; I have a Red spruce ('Adirondack') top that has the same density as a Western Red Cedar top in my stash, and they both have the same Young's modulus along the grain. When I use them I'll make them the same thickness if I'm making the same model of guitar.