Bourdon (organ pipe)
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Bourdon, bordun, or bordone normally denotes a stopped flute/flue type of pipe in an organ characterized by a very dark, heavy tone, strong in fundamental, with a quint transient but relatively little overtone development. Its half-length construction make it especially well suited to low pitches, and the name is derived from the French word for 'bumble-bee' or 'buzz'.
This stop is most commonly found in the manuals and the pedal at 16′ pitch. Since Bourdons are stopped pipes, they are only half the length of an open pipe of the same pitch. It is also common in the pedal division at 32′ pitch, where its very heavy roll of sound can actually shake the building it is installed in. When installed in the pedal division, it is often known as Subbass or Soubasse (Fr.).
It can also be found at 8′, especially in French organs; in other organs the Gedackt and stopped Diapason, which give a similar sound, usually takes its place. Although sometimes varying between builders, its tone is usually low pitched and firm.
The pipes can be built of wood or metal, but are overwhelmingly constructed of wood in modern organ building (French makers from Cavaille-coll on prefer metal). They are thick walled, and generally square in cross section, with a high mouth cut-up to produce the fluty tone. Bourdon is a stopped pipe, having an airtight stopper fitted into the top. This both makes the tone one octave lower than a similar pipe of open construction, and also eliminates the development of even-numbered harmonics ("squaring off" the timbre), helping to create the characteristic dark tone.
This stop is very common in church organs and indeed theatre organs. The Bourdon is the most commonly used organ stop for Bach cantatas. In an organ so small as to have only one 16′ stop in the pedal division, it will almost invariably be a bourdon, as the deep, dark and penetrating tone can be clearly heard under soft or loud combinations, and blends well with all sounds of the organ.
'Bourdon' has many spellings and German organ builders will often use "Bordun", or even "Untersatz" (typically when it's in the pedals) on the stop knob for this rank. "Subbass" was originally a stop of somewhat different design than the Bourdon, but the word is accepted today as a synonym for a Bourdon in the pedals. The Italian spelling is "bordone".