It is a large-scale, stopped wood flute pipe, usually with a leathered lip.
Tibia Clausas provides the basic foundation tone of the organ with few overtones or harmonics.
The stop shares similarities with the Bourdon and the Gedackt found in some church pipe organs.
In smaller organs, a Bourdon or Stopped Diapason may be substituted for a Tibia Clausa at 16 ft (4.9 m) pitch.
This article relating to free reed aerophones is a stub.