The Japanese flute called a Hochiku is similar to a shakuhachi and is often lumped in with the shakuhachi. But Tom Deaver, in Japan, points out that the two are different and explains this difference.
Hochiku, or as some write, Hocchiku, flutes are always (except for the exceptions) one piece flutes, without the familiar connecting joint near the center of the length. Shakuhachi are almost always made in two pieces with the joint near the center of the length. Any shakuhachi made in one piece is called "nobe". The "be" of "nobe" sounds like the "ba" of "baby". "Nobe" can be translated into English as "total".
So, hochiku are a simpler, more natural flute than the shakuhachi. It could well be that 'improvements' to the hochiku resulted in the shakuhachi. Anyway, hochiku makers fiddle with the nodal membranes-- selectively filing them away to achieve certain desired tonal properties. Unfortunately, the process isn't easily reversible. You're working down the bore with special tools and if you go a little too far in the filing then what?
Well, you can probably see where this is going. The obvious answer would be tunable nodal membranes--and that's what we're going to build. Using gray 3/4" schedule 40 PVC we'll fashion a hochiku with special adjustable 'nodal membranes'.
Where do the nodes go? Many years ago, XELO, a radio station streaming out of Chihuahua, Mexico sold live baby chicks through the mail. Part of the spiel was, "You can grow 'em up, bash 'em on the head, eat 'em if you want. You can do anything you want wit 'em, cuz they yo' chickens." The nodes is yo' chickens.You can put a node any place you want. And put in as many nodes as you want.
Generally there are four nodes if we count the closely spaced nodes at the foot of the flute as one. Since a shakuhachi usually alters the location of the fourth node when the top section is cut and reconfiured this node location is based on aesthetics rather than the natural growth pattern. What are the natural growth nodal locations? Hard to say because culms for hochiku are selected by at least partially aesthetic criteria. But we're really only talking about one node--the fourth (see table below). Where should it go? It will be closer to the mouth than it's located in a shakuhachi. Let's say 24 mm. Again, you can put any and all nodal membranes wherever you wish. Make up your own natural nodal algorithm or measure a prized piece of bamboo and use those ratios.
All measurements in millimeters and from the top.
This length (576 mm) with an integral mouthpiece plays C#.
So you can skip the nodal business
and just build a C# flute from these measurements.
Cut the pipe, fashion the mouthpiece, drill the holes 3/8" and mark the node holes along the underside of the flute. Drill and tap the node holes to accept 1/4" inch bolts. Insert the bolts and you've got a tunable hochiku--just screw these 'nodal membranes' in and out as you wish. That's the concept. You can easily alter location and number of nodal membranes along with their size and material. Small Parts, Inc sells nylon setscrews of different sizes and lengths. Air seal the bolts with Vasoline or wax.
There have been claims that adding outer 'nodes' to PVC will improve it tone. The theory is that PVC needs stregthening at nodal locations to achieve full resonance. If that's true then hose clamps would do the trick. We're all little more inclined to believe that adding mass at selected points along the course of the flute might effect it's resonance. In any event, the size and material of the bolts lend themselves to an investigation of the role of mass in this mysterious subject of 'resonance'.
Screwing bolts in and out at selected locations changes the volume of the bore which has a direct effect on sound and tuning. It's called perturbation and that's what filing natural nodal mebranes does. One interesting aspect of this design is that with a partner you can actually hear the shift in tone as the bolts are being adjusted during play--real time feedback.
These hochiku are inexpensive, simple to build and lend themselves to learning about nodal membrane tuning--besides worrying the neighbors. A different kind of adjustable flute is on the Throated Flute page.
See The Synthesis for a final flute design.