Shaku
Design
Searching for the Edge

Updated 4/24/08

You want to know something about the mystery of the Shakuhachi? Much of it can be found in the mystery of the airstream. Let's first talk about what you need for a basic flute. You need an air stream, an edge and a resonator. That's about it. To make a flute work, direct an airstream onto an edge which is coupled with a resonator (usually a tube of some kind) and a sound results. Simple, right? Well, maybe--kind of.

Since we're talking generally about the Shakuhachi, we're talking about an airstream formed by the lips (and maybe the mouth, throat, lungs, etc.). Let me say maybe because it turns out this airstream isn't a simple affair and isn't understood very well. The thing waves and flaps around--something like a flag in the wind. And why does a flag flap in the wind?

Two Zen monks were arguing about a flag. One said, "The flag is moving." The other said, "The wind is moving." The Sixth Patriarch happened to be passing by and he told them, "Not wind, not flag; mind is moving."

Jun Zhang, a physicist at New York University, has a slightly different answer as can be seen in the graphic below.

We're not going to settle the flag debate here, but will adopt the preceding graphic as something conceptually close to what the airstream looks like. As the airstream moves from left to right it flaps up and down. Why? It just does.

First, let's combine an airstream with an edge. Blow on the edge of a credit card. Actually dig one out and blow on it. What do you hear? Kind of a hiss? Good. This is called edge tone(s). Why does blowing on the edge create a sound? It just does. If you need some kind of explanation, it's the flapping of the airstream which flaps above and then below the edge. But how does this result in a sound? We're back to where we started--it just does. Here's the point of this paragraph: An airstream naturally has a dynamic turbulent flow something like the graphic above. It's non-linear and for the most part, unstable. The thing is alive and sensitive to most any influence. You can employ the Navier-Stokes equations, Reynold's Number, spread on a good layer of Bernoulli, and/or learn Chaos Theory and mess with bifurcating points--but you'll just end up with the fact that the thing's alive and sensitive to most any influence.

Blow on an edge and you get edge tones. What are they? For the most part they're white noise--a packet of random frequencies. Couple white noise with a resonator (a tube which is tuned by its length ) and you get a stable tone. So the tube does two things: It's a filter which filters out all but a selected frequency and an amplifier, amplifying that frequency. A small fact you can tuck away in the back of your mind: A flute is about 1% efficient in turning the energy of the airstream into defined sound. Only about one percent of what you blow ever gets turned into anything you wanted to hear.

The airstream follows its own will-o'-the-wisp path, easily influenced by everything around it. Have a bushy moustache, for example? This can make a big difference in the flow pattern of the airstream. This is what Joe Wolfe is getting at talking about 'face' impedance.The tube is fixed and not very influenced by anything except the holes which just change the tube's length. And between these two we have the edge.

So what kind of edge is best? Surprisingly, it doesn't make a lot of difference. Don't believe me? Blow on other edges besides credit cards. Razor blades, thin paper, the edge on your ruler, the edge of different kinds of files (the ones in your workshop), the edge of quarter inch plywood. Blow across a pencil, nails, the edge of floor tile. You hear anything dramatically different? Nope. Just that hiss--white noise, also called aeolian tones. Now, if you do this experiment and do it carefully you'll notice that the general frequency (if there is such a thing) of the edge tones is lower when the edge is thicker. That's about the only difference you'll find with edge tones. And in fact, there's an equation for it--frequency is inversely proportional to edge thickness.

Still don't believe it? Try edges of different geometries. Round ones, square ones. Tapered, sharp, blunt, etc. Try them all and you'll get about the same sound. Which means that the edge in a Shakuhachi perhaps doesn't make as much difference as you might have thought. Yes, different kinds of edges may do slightly different things--but not dramatically so.

Still not ready to give up? Try rough edges, polished edges and anything else you can think of. And in the end you'll come to realize that the graphic above is the way it is regardless of the edge. The Shakuhachi sounds the way it does in large part because it exploits the natural instability of a dramatically turbulent airstream. So we've moved from the tube to the edge and finally to the airstream. What controls the airstream? As much as it can be controlled it's controlled by the lips--the embouchure. The airstream in a recorder or a pipe organ is about as controlled as an airstream can be. The thickness, width and distance from the edge are all fixed and about all that's left up to the player is the air pressure. With a Shakuhachi all this is within the player's control. So if you're seeking a better sound and are offered a better instrument or better embouchure--choose the lips.

And speaking of lips, whistle just using your lips. Where does the sound come from? No edge, no resonator. Ready to accept the possibility that there's plenty going on just with lips and airstreams?

Adopting a flame analogy, the flame of a candle is fairly stable and quiescent, while the flame of a campfire is turbulent and unpredictable--airstreams are the same. At very low pressure and speed airstreams are quiet and steady like a candle flame, but at the pressure and speed at which most playing is done they're wild like a campfire flame. And much of the Shakuhachi's sound and possible effects exist only because of the airstream's turbulence. So a Shakuhachi is an instrument designed to make aurally present the turbulence of a flame of air--to make flames speak. To squeeze this analogy even further, campfires make a sound--yes, low frequency white noise.

So feel free to experiment with different edge configurations and/or don't worry too much about achieving a particular configuration.

For some precise hole measurements and instructions leading to some great practice shaks visit PVC Shakuhachi. The Aspect Ratio's role in the sound of the shakuhachi becomes clear in these examples.

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