Sets of dissimilar flutes with internal duct
Sets of open flutes with internal duct
Sets of stopped flutes with internal duct
Sets of partly-stopped flutes with internal duct
Flutes with internal duct
Sets of flutes with internal duct
The air itself is the vibrator in the primary sense. The standing waves are significantly confined within each flute, where a narrow duct directs the air stream against the sharp edge of a lateral orifice. Two or more flutes are combined to form a set.
Hornbostel - Sachs