Wes Paul wrote:
I was told by another builder that he always uses the same kind of wood for bracing as for the top. He says once he used a cedar top with spruce bracing and it came back concave. He did say the guy had let it dry out to much but that he tried to humidify it and it didnt work as it usually does. He said that after that he always used the same bracing as the top and has never had problems.
That makes no sense at all
Sounds to me like it was probably an early build without humidity control, and braced in really high humidity, with the cause of trouble being misdiagnosed. The braces change very little with humidity, so the species shouldn't matter. There is a certain elegance to matching top and brace woods, but ever since reading in the Gore/Gilet book that stronger woods are more creep resistant, I've been sticking with spruce. Due to the low density, tall cedar braces can be a bit lighter weight than spruce braces carved to the same stiffness. But they'll still creep faster due to the lower strength.
I built two with redwood braces: one small classical, and one steel string harp ukulele, both in 2012. The classical is fine, but the harp uke is pretty warped. Not sure exactly how much is due to the brace species versus just carving them too low, but I'll be avoiding redwood and cedar braces in the future. They split more easily, too.