arched back vs flat back

[Happy Builder]

almost all plans have curved or arched back

whats wrong with flat back

was planning a new instrument will both do or with with arched

[Steve Beckwith]

Curved/arched/radius-ed surface have better structural integrity than a flat top.

[Rory]

Not sure what your building, but it is done. Check out Lawrence Nyberg- he does carved top bouzoukis with flat (but domed) back. He says it brings out better projection and volume than carved backs. Im sure the results are different for different instruments, but it is done. If you mean totally, totally flat, usually some curvature is desirable for strength but Ive seen some cheaper guitars with truly flat backs. It takes very little time to put a bit of radius on the back braces so why not give it a bit of a dome?

Rory