The graphic above plots hole size equivalent to hole timbres of the 1.8 shakuhachi. Examples are given in 1/2 millimeter steps from 9.5 to 11.5 mm. Each line depicts equivalent hole timbre across a range of flute lengths. For example, a 10mm hole size on a 1.8 (blue line) needs to increase to 12 mm on a 2.4 flute to maintain the same hole timbre and balance. With longer flutes the acoustical properties of holes run up against the limits of finger size and it shouldn't be surprising that these flutes are often characterized as mellow and mysterious as, generally, their holes are undersized.

For the sake of this discussion consider a 10.5 mm hole on a 1.8 to be optimal. Increasing hole size to 11 or 11.5 mm will make the 1.8 flute sound louder, shriller, bright and brassy--the higher harmonics are accentuated . Decreasing hole size will sound mellow, quiet, and dark as fundamental harmonics are boosted. And, of course, changing hole size will move hole location along the barrel of your flute--smaller holes move toward the head of the flute and larger holes migrate toward the foot.

To use the graph, find the place on the graph which represents a favorite flute. The colored lines will automatically extend your hole timbre to different length flutes.

The point of this page is that using similarly sized holes across a range of flute lengths has substantial impact on timbre. To maintain similar timbre with different lengths, hole size needs to be matched to length--hence bore. Hole size doesn't change at the same rate as length, but the two are definitely related. Use of the proper formulas and this graph can aid significantly in designing and building flutes with chosen acoustical properties.

The formula for optimal hole size (listed on the Magic Flute Formulas page) produces a hole size of 10.507mm (green line in the graph above) for the 1.8 shakuhachi.