These pages comprise a dictionary of terms relating to the pipe organ. Please keep definitions to a few sentences, and do not include pictures or sound clips. When more space is needed for a term, a new page can be created for it.
Unda Maris - see Voix Celeste
Unification [noun] a technique whereby many stops share a small number of ranks, with each rank being used on multiple keyboards at a variety of pitches. Theatre organs use unification heavily, but is not desirable on classical organs except as an extreme cost- or space-saving technique.
Unison Off - An intra-manual "coupler" which removes the nominal pitch and leaves only the sound from the octave and/or sub-octave coupler. Thus the performer could "create" an 8' flute on the Swell by drawing a 4' flute, the Swell to Swell 16' coupler, and the unison off. Without the 16' coupler, there would be no sound. A device exclusive to electric-action instruments.
Unit Chest [noun] - a type of wind chest in which each pipe has its own electric or electro-pneumatic valve.
Universal Wind Chest [noun] - a type of wind chest patented by the Austin Organ Company, characterized by being large enough to walk inside for maintenance, even with the wind on. These chests are usually fitted with airlocks for access while the wind pressure is up.
Unterwerk [German, noun] - A section of an organ that is situated under or beneath other sections in the case. Although it is likely to be subordinate to the Hauptwerk, the name refers only to its placement within the case. See Oberwerk.