Mujitsu and Tairaku's Shakuhachi BBQ

Mujitsu wrote:

One common practice to improve tone is to open up the bore slightly at approximately 3cm from the top end. Perhaps there is a connection there.

That's a strong possibility. As I thought about this while drifting off to sleep last night, I began to think that a grove on the outside of the flute probably wouldn't make any difference at all. The groove would have to go IN the bore in order for it to affect the tone (duh). What had me confused for a second was the fact that the navaching illustration has a reverse cut utaguchi where the 30 degree slant is inwards towards the bore.

Ken- Is opening the bore at 3cm intended to make the flute sound better or make it easier to play? Or is it both? I have a feeling this is related to my question somehow. If it had more to do with tone, I would think you would open the bore at a percentage of the flute length, rather than 3cm across the board for any flute. A standard measurement would indicate to me that it's more of an airfoil thing going on to increase the aerodynamic efficiency of the utaguchi.

Last edited by tingjunkie (2010-01-26 17:50:22)

Mujitsu wrote:

It can give the tone of a flute more presence, depth, power and sustain. I imagine that might make it "easier" to play.

...I could have been clearer there. The 3cm approximate measurement is for a 1.8 shakuhachi. On longer flutes it can be more since it is based on its length.
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Ok, sounds like the same general principal. Thanks for the info Ken. May I ask what tool(s) you use to remove material from the inside of the bore? Do you remove material all the way around in a circle, or only below the utaguchi?

Here's a shot of some sanding drums. They can also be attached to long rods and used with a drill.

I generally like Navaching but I think he is blowing hot air on this anti-stall business. It is important to understand that a flute and an airplane wing are very different things, due to the fact that the air jet leaving the player's lips and striking the blowing edge is affected by what is happening in the tube, whereas there is no analogous situation with an airfoil.

Here is a quote from the UNSW site on flute acoustics:

"The jet of air from the player's lips travels across the embouchure-hole opening and strikes against the sharp further edge of the hole. If such a jet is disturbed, then a wave-like displacement travels along it and deflects it so that it may blow either into or out of the embouchure hole. The speed of this displacement wave on the jet is just about half the air-speed of the jet itself (which is typically in the range 20 to 60 metres per second, depending on the air pressure in the player's mouth). The origin of the disturbance of the jet is the sound vibration in the flute tube, which causes air to flow into and out of the embouchure hole. If the jet speed is carefully matched to the frequency of the note being played, then the jet will flow into and out of the embouchure hole at its further edge in just the right phase to reinforce the sound and cause the flute to produce a sustained note. To play a high note, the travel time of waves on the jet must be reduced to match the higher frequency, and this is done by increasing the blowing pressure (which increases the jet speed) and moving the lips forward to shorten the distance along the jet to the edge of the embouchure hole. These are the adjustments that you gradually learn to make automatically when playing the flute. Flutists are usually taught to reduce the lip aperture when playing high notes."

The important thing to understand in this is that the jet must strike the edge in a way that it can flow either into the tube or outside of it, and there is a wide range of angles in which this can happen *as long as the jet is aimed precisely at the blowing edge and maintains the correct distance/airspeed ratio so that the jet timing is correct to allow a deflection to occur depending on what is happening in the tube.*

And what is happening in the tube is that a compression wave is moving end to end. In order to reinforce this compression wave (and thus create a standing wave oscillation) each time the wave hits the top of the tube, the air jet, as mentioned, needs to have a certain speed and/or length, so that the oscillation of the jet in and out of the tube is proportional to the speed of the wave inside the tube.  When this condition is met, the jet can give the wave in the tube a kick each time it arrives at the embouchure hole, while at the same time the wave in the tube is giving a little kick to the jet to knock it out of the tube and also keep it oscillating.

There is a pretty clear demarcation between the jet and the tube, although the jet does travel a small way into the tube before dispersing into turbulent vorticies. So what Nelson Zink is saying doesn't make any sense to me, because he is talking about tube territory, not jet territory, and this would affect the harmonic modes of the tube much more than the jet itself, at least insofar as I can see. Reynolds numbers and turbulence are a different matter altogether, and turbulence at the edge can produce noise, but that does not generally affect the jet in the way Zink describes it.

Toby

Last edited by Toby (2010-01-30 04:57:33)

Yes, that's basically correct. The other element is that when the wave inside the tube deflects the jet to the outside, it sends a disturbance up the jet itself, and that must also be in phase with the wave inside the tube in order for the jet modulation to reinforce the wave in the tube. That being in phase depends on two things, the speed of the air and the length of the jet. The air velocity is a second order function of the pressure, so that means that to achieve twice the velocity, one has to blow 4x as hard. Therefore, flute players achieve the higher modes by both blowing somewhat (but not 4x) harder and moving the lips closer to the edge to reduce the jet length. The fact that either or both of those methods achieve the correct result (the correct phase of the jet in relation to the wave in the tube) means that the player has quite a range of expressiveness to play with, as the two methods produce quite different results in terms of intonation and timbre.

Have a look here:

http://www.phys.unsw.edu.au/jw/fluteacoustics.html

Even those this is specifically about the side-blown flute, most of it applies to endblown flutes as well.

This is sketchy, but specifically about the shakuhachi:

http://www.phys.unsw.edu.au/jw/shakuhachiresults.html

Toby

Why doesn't any one try it? There is a picture on Nelzon Zink's website of a utaguchi with the air foil. He has probably tried it, which is why it is on his website. But the only way to know for sure is to do it. Theory and practice do have a difference. Just take a piece of PVC, try it, and post how it goes. I would if I had the PVC or the tools to do it.