I’d like to know more about undercutting
in the making of flutes. Really all I know
is what I can infer from the word
and the info that embouchure holes
and tone holes are what is undercut. Anyone?
Simple, in theory at least, the hole is smaller on the outside than it is on the inside of the bore. This allows a bigger break in the vibrating column of air to give a true note. Changing the size of the holes on an existing flute will of course put them out of tune with each other. You need to start by copying an undercut flute (Hawkes or Boosey for example) to understand the physics. The F# hole on an 1860’s Boosey is so big if you take the undercutting into account it’s probably almost the same diameter as the bore.
Ken
Undercutting helps with the “Phase-shift” between registers Jim. There are places of highest vibration for each frequency wavelength called “anti-nodes” or “loops”. Because of air column velocity changes between registers, these “cut-off frequency nodes” shift a little up and down the bore and the air column can “pass by” a narrow opening on the inside of the bore resulting in weak tone.
By using a truncated cone shaped tonehole, a designer can “stretch out” the inner opening of a tonehole so the shifting of these nodes will have little effect on a tonehole’s acoustic energy.