Just a correction, `harmonic frequency` and `overtone` are something
slightly different. Hormonic indicates a direct multiplication but overtone, although very close to harmonic frequency but not necessarily.
So, the right word should be 3rd overtone or 5th overtone crystal not 3rd harmonic crystal.

By the way, Peter Dannegger`s view is rather viable that I tried a while ago upon his advice.

Rustu Kaya