And if that tuning drifts too much, not only does tuning of the instrument suffer, but so does response. So important to attend to it.
Yes, the cylindrical bore flutes seem to want
slightly bigger holes in general to play well and in tune. Plus it gives the flutes a big voice, which might be desirable in some instances. Blayne described one of these as a potential "session cannon" because the voice was so strong and could be pushed. But I suspect most ITM players who play in sessions are going to lean toward the conical bore versions, simply because it's familiar and traditional.
You might want to experiment with a different head taper as an alternative to making the tone holes uncomfortably big. I have no reason to believe that Boehm's head taper is magical. I'd guess is that it worked for him with the size of holes he chose. We know that no taper (i.e. simple cylinder) makes for very flat harmonics. So more taper would presumably give sharper harmonics, and permit smaller holes.
It's funny you should mention this, because I have at times pondered on the subject along the way as I messed about with different ways to introduce the taper. It was that bamboo flute that got me thinking because I'm quite confident that the natural taper in that piece of bamboo does not follow the ideal as outlined by Theobald Boehm. And yet it works beautifully. So it would make for an interesting experiment to try variations on the taper. The thing that would inhibit this experiment (and most makers who create their own tooling will appreciate this) is that making reamers is a lot of work! To experiment with a bunch of taper variations means manufacturing a bunch of reamers which is not an easy thing to fit into a busy schedule, especially when there is no certainty of an improvement.
But, consider a cross-section cut through at the embouchure hole. The bore won't be round, it will be D-shaped. And remember our flute is side-blown, so the top end of the vibrating air column has some spiral elements. I'm guessing that our D-shaped bore is introducing some aerodynamic inelegance.
Exactly! My feeling was that by introducing the taper and creating that D-shape it introduced some type of turbulence or resistance to the easy flow of air. I tried to counter this by moving the taper around a big in relation to the embouchure hole, but it didn't change anything much. Again, it was not so bad as to be a deal breaker, but when I compared it to a reamed head I could tell the difference.
I did think of another work-around for those not wanting to go to reaming. You could make a tapered former, grease it well with release agent, poke it up the cylindrical head, and pour epoxy or something similar into the stopper end. After the potting agent dries, you remove the former, leaving a nicely formed tapered bore.
Definitely a workable solution. You'd have to come up with a reasonable method of centering the former in the bore in a way that would still allow you to introduce the epoxy, but that is do-able.