Bamboo flutes need to have the inner nodes (the diaphragms) removed in order to form a tube. Partial removal of the diaphragms allows for tuning opportunities by way of perturbation. For root-end culms, nodal location is in the vicinity of 1/3, 3/5, and 4/5 of the total flute length. Cutting/sanding away partially removed diaphragms will affect a flute's tuning, hence the practice of Nodal Tuning.

Often, tuning diagrams indicate that a note's wavelength ends at the hole, but it runs past the hole as indicated. To get an accurate picture, the wavelengths must be represented correctly as they are below.

Removing material where the blue wavelength is above the red line FLATTENS the pitch. When the blue wavelength is below the red line the pitch SHARPENS. When the blue wavelength is near the red line or crossing the red line little pitch change takes place (X). As can be seen in these tuning graphics, removing material sharpens some notes while at the same time flattening others. And to be clear, removing (or adding) material anywhere in the upper half of the flute affects ALL notes. In the upper half of the flute you can't adjust the bore just to fix one or two notes, they're all affected--some more than others and not always in the same direction.

Short wavelengths (higher notes) are affected more than longer wavelengths (lower notes). And the location (along the bore) of the diaphragms is of significant importance as can be seen after study of the tuning graphics.

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The first node (the one closest to the head of the flute) affects all the notes as it's in the upper half of the bore. For nodal tuning it's the most important. Since the location of nodes varies considerably between culms each flute needs to be thought about separately. Apparently, it isn't bamboo's primary intention to become a flute.

Ro otsu

2

3

4

5

6

Ro kan

7

8

9

10

11

First Node

X

F-

F

F+

F

F

F-

X

S

S+

S

F-

Second Node

F

X

X

S

X

F+

F

S

Third Node

X

S+

F

S

It's vitally important to know where the nodes are in relation to the bore length, which is to say, in relation to the wavelengths. Once the first node is marked on the graphic at the end of this page, the change in pitch for every note can be predicted and notated. Removing more of the diaphragm just moves each note further in the direction it was going. The degree of perturbation (both flat and sharp) is largely determined by how near to the center of the wave-crest the node falls.

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There is a way around the limitations inherent in nodal tuning:

1) Remove all nodal diaphragms until the bore wall is flush.

2) Tune the first octave slightly flat progressing upward from Ro-otsu. This is most easily done by working on the holes. Tip the first octave so that it gets progressively flatter.

3) There is a single place in the bore where perturbation affects all the notes in a smooth and progressive way--at 1/8 the length. Nowhere else in the bore is this possible. Adding material at this point flattens the low notes and sharpens the high notes, so Ro-otsu (etc.) is flattened and octave balance is achieved. Adding material at this special place tips the first octave back to where it should be and the second octave is progressivly sharpened, bringing it into balance. This spot can be up to an inch long so the bore addition should be from 1/2" to 1" long. Bore addition works backwards from bore subtraction as far as tuning goes, so the following tuning graphic below works differently (opposite) from the two above.

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Download to desktop, print out and use to plan tuning.

There are four cases: Above, Below, Add and Subract.
On the Tuning Chart are reminders as to how the cases resolve to either Sharpen or Flatten.
Mark nodes or additions/subtrations and determine how each will affect the flute's scale.

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