Vessel Flutes: In the Hornbostel-Sachs classification system vessel flutes are those whose body behaves as a Helmholtz resonator. Such a body on these instruments are vessel shaped in the following designs [egg shaped as in the Chinese Xun, cone shaped as in the Ocarina].
Types of vessel flutes: These flutes have a fipple to direct the air at an edge. This side of the vessel flute sub-category includes the Gemshorn, Pifana, Ocarina, Molinukai, Tonnette and Niwawu.
Behaviour of vessel flutes: When a vessel flute is played; the air in the body of a vessel flute resonates as one. With the air moving alternately in and out of the vessel, and pressure inside the vessel increasing and decreasing.
Blowing across the opening of empty bottle produces a basic edge-blown vessel flute. Multi-note vessel flutes include the ocarina.