An overtone flute is a type of a flute that is designed to play in the upper harmonics, typically well above the two or three harmonics that are the practical limit for most woodwind instruments.
An overtone flute has either no tone holes,[2] or relatively few tone holes for a woodwind instrument.[3] To make melodies, one plays it high into the overtone series. One series of harmonics is achieved by overblowing with the end of the tube open and another is achieved with the end closed; when the end of the flute is closed, the key drops by one octave and only the uneven harmonics can pop out. 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.
