Vance, and all, I have a sneaky feeling that the shape and air mass are a small part of the equation. The vibrating chararistics of the wood of the body and soundboard would also be part. The sound hole should be minimal as a "projecting" matter, although significant as a "release" of pressure. (I think I mentioned that the South American harp has a "access hole" in the base, since the back is made like a lute - whereas the European and Celtic harps have the access in the back - and neither has a "sound hole"). I'm sure the the great luthiers did understand (empirically if not theoretically) the combination of size, shape and materials when it came to resonance. But even small variations in the soundboard wood and thickness (and the body) should also have affected the RF, so some instruments made the same way could be different in musical quality.
Best, Jon
