- Tibia Clausa
A Tibia Clausa 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 Tibia Clausa is arguably the most important rank of pipes in a theatre pipe organ, with some organs having as many as 5. The stop shares similarities with the "Bourdon" and the "
Gedackt " found in some church pipe organs. In the 18th and 19th centuries, Tibia Clausa was sometimes used as an alternate name forDoppelflüte . Most tibias are made from wood, although a few examples of metal tibias may be found.The Tibia Clausa, or Tibia, is generally found at 16′, 8′, 4′ and 2′ pitches as a unified rank. The mutation ranks Tibia Quint 5 1/3′,
Nazard 2 2/3′ and Tierce 1 3/5′ are also drawn from this unified rank of 97 pipes. In some larger organs, a second Tibia rank may be present, extended to 1′ instead of 16′, allowing a 1 1/3′ Nineteenth mutation and a 1′ Piccolo to be drawn from this rank. A few of the largest theatre organs, and some church organs, may have a separate 32′ Tibia Clausa rank of 12 pipes. In smaller organs, a "Bourdon" or "Stopped Diapason" may be substituted for a Tibia Clausa at 16′ pitch.The Tibia may be voiced on wind pressures from 10″ to 25″ WP (water pressure). The Tibia is generally used as a chorus stop, with or without tremulant; it is not normally used as a solo stop due to its relatively dull tone.
Other variants of the Tibia Clausa include: Tibia Bass, Tibia Flute, Tibia Major, Tibia Plena (open tibia) and Tibia Rex.
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