Black Tennis Pros

A set of pipes all having the same tone quality is called a rank. The most characteristic organ sound is produced by metal flue pipes called diapasons or principals; pipes of this kind form the central core of classic organ sound. Because the lowest note on most organs (two octaves below middle C) is produced by an open diapason pipe about 8 ft long, ranks of pipes at normal pitch are spoken of as 8-ft ranks. Ranks sounding an octave lower than normal are called 16-ft ranks, and those sounding an octave higher, 4-ft ranks. Mutations are ranks of pipes sounding at pitches other than octaves above normal pitch, such as an octave and a fifth above normal (for example, two G's above a C). Mixtures are ranks of pipes of different pitches operated as a single unit (by a single stop). Mixtures often contain ranks sounding several octaves above 8-ft pitch as well as mutation ranks. The high pitches of mutations and mixtures blend together to produce the incisive, bright quality that is associated with organ sound.

On large organs the ranks are grouped together into several divisions, each controlled by a separate keyboard, or manual, and having one or more wind chests, airtight boxes that act as air reservoirs. The main division is called the Great Organ; the other most common divisions are the Choir Organ, the Swell Organ, and the Pedal Organ. The pipes of the Swell Organ are enclosed in a “swell box,” a chamber having a slat-covered opening similar to a venetian blind. The slats can be opened and closed by a pedal lever, allowing gradual changes in volume.