Triple contrabass viol
The triple contrabass viol is a modern variant of the French octobass, which lost favor with most composers since its creation in 1850. It is an acoustic string instrument belonging to the family of the violin, viola, and cello. It is more closely related, however, to the double-bass, known as the viol family.
Recordings and performances of sub-contrabass string instruments are rare; over 10 feet tall, the triple contrabass viol must be played with the performer on an elevated platform. It was originally a three-stringed baroque instrument tuned C0-G0-C1 or C0-G0-D1 with the lower C coming in at 16.35 Hz. This is equivalent to the C two octaves below the cello's lowest C.
It is known that a four-string variant has been played recently by bassist Brian Smith for a Roscoe Mitchell recording. It had two large circular holes in the body to facilitate recording.