The Subcontrabass Saxophone
The subcontrabass saxophone is a type of saxophone that Adolphe Sax patented and planned to build but never constructed. Sax called this imagined instrument saxophone bourdon (named after the lowest stop on the pipe organ). It would have been a transposing instrument pitched in B♭, one octave below the bass saxophone and two octaves below the tenor saxophone.
Until 1999, no genuine, playable sub contrabass saxophones were made, though at least two gigantic saxophones seem to have been built solely for show. Although the smaller of the two (constructed in the mid-1960s) was able to produce musical tones, with assistants opening and closing its pads due to the instrument's lack of keywork, witnesses have stated that it was incapable of playing even a simple scale.
The B♭ subcontrabass Tubax, which was developed in 2000 by instrument manufacturer Benedikt Eppelsheim of Munich, Germany, is described by Eppelsheim as a "subcontrabass saxophone". This instrument is available in both C and B♭, with the B♭ model providing the same pitch range as the saxophone bourdon would have. A contrabass-range Tubax in E♭ is also available.
The question of whether or not the Tubax is truly a saxophone is debatable: it has the same fingering as a contrabass saxophone, but its bore, though conical, is narrower (relative to its length) than that of a regular saxophone. This makes for a more compact instrument with a "reedier" and "fatter" timbre. While some argue that the Tubax is akin to the double-reed sarrusophone, the Tubax's bore is much larger than that of the corresponding size of sarrusophone. Some authorities regard the Tubax as a separate family of instruments rather than as a type of saxophone.