Double bass varies considerably in size, the largest normally being under 6 feet (1.8 metres) in total length. The body itself, without the neck, may be up to 4.5 feet (1.4 metres) for a full-size instrument, about 3.8 feet (1.2 metres) for a three-quarter size, and only slightly larger than a cello for the small chamber bass, or bassetto.

A double bass is usually strung with four heavy strings pitched E1–A1–D–G; a fifth string is occasionally added—in jazz band basses, at the top of the register to allow high notes to be played more easily; in symphony orchestra basses, below the E string, tuned to C. Many basses, rather than having a fifth string, have a mechanical device with levers that increases the length of the fourth string. With this device the pitch of the E string may be lowered to E♭, D, D♭, or C, or clamped to sound E when the lower notes are not needed.

Double bass, also called contrabass, string bass, bass, bass viol, bass fiddle, or bull fiddle, French contrebasse, German Kontrabass, stringed musical instrument, the lowest-pitched member of the violin family, sounding an octave lower than the cello. It has two basic designs—one shaped like a viol (or viola da gamba) and the other like a violin—but there are other designs, such as that of a guitar.

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