How many times have you looked down inside a shakuhachi and wondered: "Just where does that sound come from?" Why does every piece of bamboo have a unique sound and for that matter, why does the same flute played by two different people sound different?" The movement of air inside a shakuhachi is of quantum-boggling complexity, but there is a beauty and order to the natural universe that is magical.
So let's talk about magic: air molecules are constantly banging around and in a small chamber such as a shakuhachi bore they bounce off the walls creating a slightly higher pressure. When you blow into the flute the air bunches up and springs back-- it's very elastic stuff. As you blow over a sharp edge, the air bunches then springs back and helps to redirect the blowing slightly "out" of the flute, then back "in" the flute in a fast sequence that reinforces itself and sets up the vibrations we hear as sound.
The point where the air bunches together most (before springing back) is approximately half-way down a vibrating tube and is the acoustic equivalent of the center point of a vibrating string, the point which has the greatest movement. On shakuhachi, I call these "pressure points", although they are more accurately called points of the most intensification and most rarefication (when the air springs back in both directions the pressure is lowered).
As the most dynamically active point or place in the bore for any given tube length, this is the most important spot. If it is a little too big or small (to the order of .02mm!) the vibration may not resonate easily. However, like problems encountered at a large family gathering, everything is relative, bores are only small or large in relation to their surroundings, and other usually unimportant factors can affect the balance of the gathering.
Everything about the bore, which includes the configuration of the player's mouth, the mouth piece, and the finger holes, affects the sound. In a very real sense, when a shakuhachi maker is shaping the bore, he is shaping the sound. Add to this the personal preference of such important tone-characterizing factors as vibrato, attack, and decay and it is no wonder that no two shakuhachi players sound alike!
Trying to make sense of all this is like driving around at night in Tokyo without lights: there are a few road signs, but without more light we are still lost. For those who would like their confusion clarified, I recommend to you the books listed at the end of this article, but I will give a bit more direction on how the chart works (Click here to see the chart).
Let us say that "chi otsu" (or the low octave with three holes open from the bottom) doesn't play well compared to the other notes around it. It may be that the pressure point is too small or too big; that is the first place to look. Try putting a piece of wet folded newspaper at the point to make the bore smaller. If it works, fine; if it gets radically worse, chances are that point is too small (relatively speaking of course).
Now it may be that it is in fact the "chi kan" point(s) (for the higher octave there are two pressure points) that is too small or too big and negatively affecting the fundamental "chi otsu." All the notes are affected by the whole tube, but such close relatives as the octave must be taken into account and influence such important things as pitch and tone color as well as the basic balance between low and high notes. In other words, depending on how the whole flute plays, it is sometimes better to make other areas smaller (or larger) so that the point that needs help will be relatively larger (or smaller). To complicate matters even more, every point you change may alter totally "unrelated" notes. Look at the chart vertically to see the interrelatedness: for example the "ro otsu" and the "chi kan" point (one of them anyway) are very close. Working out this and other puzzles to make an instrument which plays with some "balance" (definition: all notes respond well, high/low, loud/soft) is an amazing process.
One way to hear the way the chart works is by opening up the middle joining section 4 or 5 millimeters. This effectively makes the bore larger at that point. See what happens to "ro otsu" (the lowest note) and "ro kan." Check on "chi otsu" and "chi kan." Does it affect other notes as well? Push the flute together and take apart repeatedly to confirm any changes.
It is complex, but it isn't unapproachable:
the air inside a shakuhachi obeys the laws of physics in ways
you can hear for yourself. Check it out ..... the bore is interesting!
1977 The Acoustical Foundations of Music, W.W. Norton & Company, Inc., New York
Benade, Arthur H.
1976 Fundamentals of Musical Acoustics, Oxford University Press, New York
Nederveen, Cornelis J.
1969 Acoustical Aspects of Woodwind Instruments, Frits Knuf, Amsterdam
One word of caution: obviously any permanent
modifications done to a shakuhachi should be done very carefully
.... a wild bore is not easy to play with!