Overtone flute

[3] To make melodies, one plays it high into the overtone series.

This means that overtone flutes without tone holes will produce mostly the notes present in the natural scale, whilst certain notes can be bent a bit by partially covering the end of the flute.

Overtone flute tubes typically have a relatively long resonating chamber compared to their inner diameter or cross sectional area, which encourages the instrument to resonate in the higher harmonics.

An overtone flute in the key of G, with an inner diameter of 1", will require more effort to play higher harmonics than an overtone flute in the same key, with an inner diameter of 1/2".

For example, a ratio of 1 : 30 - Inner Diameter : Length allows for very high harmonics to be played with little effort.

Approximation of the notes available on a koncovka made in the key of G. Notes played with the end closed are marked with "●", and notes played with the end open are marked with "○". [ 1 ] Both groups of notes are harmonics of a fundamental on G.
Koncovka.
Koncovka, a Slovak overtone flute