The contrabass saxophone.

The contrabass saxophone is an extremely large, heavy instrument. It's huge! A real monster. It has twice the length of tubing of the baritone saxophone and its bore is twice as wide. The contrabass saxophone is the biggest existing woodwind instrument.

Imagine a woodwind instrument that goes to a low concert D-Flat, an entire octave below the baritone sax or bass clarinet. In its lowest register, the sound produced is massive and harsh. The sound is so low that listeners can have difficulty distinguishing between notes. It can be difficult to hear actual pitches.

It appears that the contrabass is the lowest real saxophone ever built. Although Adolphe Sax patented the subcontrabass saxophone, I'm not sure that any were ever actually built. It seems that what was built was more of a stage prop.

The contrabass saxophone is still produced but is quite rare.

Not many players use the instrument. It is rarely used in classical music and when used it is hardly features as a solo instrument. It has been mostly used as a solo instrument in jazz music. The instrument is difficult to hold and control, and so is actually playing it.

Contrabass players include Jay C. Easton, Thomas K. J. Mejer, Paul Cohen, Anthony Braxton, Klaas Hekman, Daniel Gordon, Scott Robinson, and Daniel Kientzy.

Personally, I like this type of saxophone. I think it fits perfectly in a saxophone ensemble. It adds to the already amazing sound of a saxophone choir. It adds an extra low end and takes you places where the baritone saxophone can't go i.e. one octave lower.

Further Reading:

Bamboo Saxophone

Electric Saxophone