The octobass is an extremely large bowedstring instrument constructed around 1850 in Paris by the French luthierJean-Baptiste Vuillaume (1798-1875). It has three strings and is essentially a larger version of the double bass (the specimen in the collection of the Musée de la Musique in Paris measures 3.48 meters in length, whereas a full size double bass is generally approximately 2 meters in length). Because of the impractically large size of its fingerboard and thickness of its strings, the strings were stopped by the use of an intricate system of hand- and foot-activated levers and pedals. The instrument was, in fact, so large that it took two musicians to play: one to bow and the other to control the "fingering", and was consequently never produced on a large scale or used much by composers (although Hector Berlioz wrote favorably about the instrument and proposed its widespread adoption). In addition to the Paris instrument, another octobass is in the Musical Instrument Museum in Phoenix, Arizona. In his edition of Berlioz's treatise (Cambridge University Press, 2002, p. 318) Hugh Macdonald lists another in the Kunsthistorisches Museum, Vienna. He also states that Adolphe Sax created an 'outsize double bass going down to C' with four strings tuned in fifths'.
Berlioz writes in his Orchestration Treatise that its lowest string is tuned to C1 (32.7 Hz), one octave below the lowest C of the cello (C2, 64.14 Hz). This note is the same as the lowest note of a modern double bass with a low C extension. The middle string is tuned to G1, a fifth above the lowest string. The uppermost string is tuned to C2, an octave above the instrument's lowest string. Berlioz quotes G2, a fifth above the top string, as the highest note playable on the instrument, giving it a compass of an octave and a fifth. However, Berlioz may have been mistaken because modern and surviving instruments are tuned C, G, C, with the low C string being 16.25 Hz (C0, one octave below the lowest C on the piano). The modern technique of octobass playing includes the technique of fingering up to A, plus higher notes possible by extended technique.