What should a shakuhachi sound like? What is optimal shakuhachi timbre? Taking the 1.8 as the standard, because it has a specific length and pitch it can only have one bore size which is right at 18mm. Given all this, the optimal timbre comes from an EAR of 30.3.

Dimensions for Optimal flutes made from PVC

There is an optimal ratio between bore and length as graphed above, but are there optimal hole locations? Probably. By adopting the Deaver Test we can arrive at a set of hole locations which are optimal for all flute lengths that can be naturally played. Which means all but those really long flutes where the holes have to be moved to facilitate your fingers. Put the holes at the following percentages (as measured from the flute head): 0.429, 0.492, 0.604, 0.691, 0.788. 43-49-60-69-79, remember those numbers and you have the hole location layout for any flute (regardless of bore size and EAR) under about 2.3 or 2.4. Or, if your memory is quirky, adopt the slightly rougher Hermit Bamboo Cutter's layout: 43-49-59-69-79.

A one percent change on a 1.8 is, at most, a little over 4mm or half a hole. The rounding error of the blue set of numbers amounts to, at most, 2mm. The blue set of numbers is all you'll ever need while making anything less than chokan flutes. You don't need to run everything through a hole location calculator which can give numbers to a ten thousandth of a percent.

The blue set of numbers applies to all flutes because the same musical scale applies to all shakuhachi.

But how can a single set of hole locations apply to all but chokan flutes?--you ask. Here's the trick, don't change the location of the holes, change the hole size. There is an optimal hole location, don't fiddle with it. Use the blue set of numbers and tune your flute by adjusting hole size. In the end you'll have the optimal location AND optimal hole size for your particular flute.

If you want to know what an optimal flute sounds like, cut a chunk of Schedule 40 3/4" PVC to 634mm, drill 3/8" holes at the blue percentages, enlarge the holes (starting at the bottom) to bring the flute into tune. You'll end up with what the long tradition of Japanese shakuhachi making has arrived at as the optimal flute. You may notice it sounds a little different from some modern shakuhachi, it'll be a little softer and more subtle.