|A lovely page on the Nohkan flute includes a section on a 'nodo' or inner throat pipe fitted into the flute's bore. It's credited with creating the "mysterious and profound" sound of the Nohkan flute. Sounds interesting. Besides, the first step in making these flutes is turning the bamboo inside out. Amazing!
The shakuhachi already has a throat of sorts--the choke point near the foot. But it only effects the base note and maybe the first couple holes--after that (third, fourth and thumb holes) the lower portion of the shak is largely irrelevant as it doesn't play much of a part in sound production. But a constriction or throat placed above all the holes would effect the sound of the entire flute.
Off to the hardware store yet again. You'll need some Schedule 40 PVC: 3/4" for the flutes and a couple feet of 1/2" for the throats. Get a 3/4" inch hardwood dowel to tap the throats in and out. The outside diameter of 1/2" PVC is slightly larger than the internal diameter of the 3/4" PVC so here's what we'll do.
1. Make a flute of 3/4" PVC (see the Shak Index for some helpful pages) For this test flute it might be easier to make it 600mm in length as most of the throat related measurements are fractions of the overall length.
2. Saw a couple sections of 1/2" PVC pipe for the throats. Cut them 1/16 of the overall flute length--or in this case about 37mm.
3. Cut through (lengthwise) one of the walls of the throat piece. This cut (or gap as it will be) should be about 3/16" wide. Ideally this is done on a table saw and the standard 1/8" saw kerf isn't quite wide enough so trim a little more. Since 1/2" PVC is too big to fit into the flute we're removing part of the throat's circumference and creating something of a spring at the same time. The finished throat will resemble what's called a 'tension pin'. Anyway, cut to these instructions and the throat will fit tightly into the flute's bore.
4. Chamfer the end of the throats and use the dowel to tap (pound?) them into position. Friction being what it is, a little WD-40 (both bore and throat) won't hurt.
From here on you're on your own. Try different lengths, different locations, etc. Put in as many throats as you want, wherever you want, any length you want. Since the basic function of the physical shakuhachi is the constriction of air in acoustically interesting ways, these throats are a natural learning and playing addition. Moving a throat a few millimeters often makes a dramatic difference. You'll end up with a lot of measuring marks on your dowel. Your flute suddenly becomes extremely adjustable. The approach used here is based on the wavelength (the length of the flute) and subdivisions thereof--which follow the formula 2 to the n. Create and explore any scheme you want.
If nothing else playing around with these nodo throats is very instructive. A tremendous amount which has been covered in other pages (timbre, Aspect Ratio, perturbation, tuning, nodes, etc.) can be experienced directly by fiddling with these throats--the theoretical made real.
Think seriously about making nodo throats (and the placement dowel) a permanent part of your PVC flute collection. With a single flute and a selection of throats you can achieve a large range of sonic effects to say nothing of a deeper understand of the whole affair.
See The Synthesis for a final flute design.