Tried the semicircle in one of the tubes I haven’t cut short yet, slightly reduced the rattle, but not by much. Again, I’ll have to re-test with shorter inserts when I see my friend again. Currently my “tuning slide” is just how far on the tube the headjoint is. I typically have them play in tune 3mm out, since most people will need to tune flat, not sharp. However, this does create a cavity between the bore immediately after the airblade and the bore of the body tube.
I feel like I’m going to end up just declaring this as “splitting hairs” from a design standpoint, but the experimental data will certainly be interesting. I like the tone of these so much that anything that alters it, even a bit, is not appealing. I might be able to move the tuning slide further south on the whistle to get away from the airblade, since the effect seems most concentrated there. I’m also testing a larger-holed design as well which will help with the octave, and I find those just sound better anyhow.
I meant “A length equal to the diameter of the bore”