It is an open, resonant wooden pipe, with a flute mouthpiece.
The pipe itself, from the mouth to the opening, is 59.2 centimetres in length, the cross section is square, 3 cm per side on the outside and on the inside from 2 at about 1.1 centimetres from the opening and then to the opening 1 cm.The side with the mouthpiece has five holes, each of which can be closed or opened from the outside by means of a rotating wooden shutter.
If the pipe is made to play the overtone of the fundamental component in correspondence to the central hole there is a vibration antinode and a node in correspondence to each of the two holes at the extremes.
Since a pressure node corresponds to a vibration antinode and, in correspondence, the air has the same pressure and density both inside and outside the pipe, on opening the central hole the pressure and density of the air inside the pipe undergo no variation and the sound emitted does not change; on opening one of the end holes, since a pressure antinode corresponds to a vibration node, the pressure on the inside tends to equal the pressure on the outside and the sound changes.
If the pipe is made to play the third harmonic of the fundamental, since there is a vibration node in correspondence to the central hole and in correspondence to the two holes adjacent to it there are two antinodes, the sound changes if the central hole is opened and remains the same if one of the adjacent holes is opened.
Battelli - Cardani (s. d.), Vol. II, p. 136
Brenni (1986), Vol. I, p. 68
Roiti (1887), Vol. I, p. 273
Segnini - Vergara Caffarelli (1990), p. 152