The double bass is a musical instrument, the largest and lowest-tuned member of the violin family of string instruments, which includes the violin, viola, and cello. It resembles the other members of the family, but is much larger and has slight differences in shape. Other names for the instrument (especially when used in folk, bluegrass, and jazz music) include string bass, acoustic bass, bass violin, doghouse bass, dog-house, bull fiddle, and upright bass. A person who plays this instrument is called a double-bassist or contrabassist.

The double bass, unlike the rest of the violin family, is derived from the viol family of instruments, in particular the Violone, a bass viol. Because of this, and also to avoid too long finger stretch, it is tuned in fourths whereas the violin, viola and cello are tuned in fifths.

The player stands or sits and holds the instrument upright, slightly tilted toward them. When standing, the top of the instrument (the head) is approximately at the same height as the players head. At the base of the double bass is a 'spike' or 'foot' which rests on the floor. As with other string instruments the double bass is played with a bow (arco) or by plucking the strings (pizzicato).

Modern instruments are usually tuned E-A-D-G, with the upper G being an octave and a fourth below middle C (approx 98Hz), and the E almost 3 octaves below middle C (the bottom E on a modern piano, approx 41Hz). A variety of tunings, and numbers of strings were used on a variety of confusingly-named instruments through the sixteenth to the early twentieth centuries, when the four-stringed tuning above became almost universal. Since the range of the double bass lies largely below the standard bass clef, it is usually notated an octave higher (hence sounding an octave lower than written). This transposition applies even when reading the tenor clef and treble clef, which are used for the instrument's upper range.

The double bass is used extensively in western classical music as a standard member of the string section of symphony orchestras and smaller string ensembles. However, it has perhaps achieved more prominence in jazz, blues, and early rock and roll where it is usually played with amplification and almost exclusively played with a form of pizzicato where the sides of the fingers are used in preference to the tips of the fingers.

In traditional jazz and swing, it is sometimes played in the slap style, a more vigorous version of pizzicato where the string is plucked so hard it then bounces off the finger board, making a distinctive sound.

Dance-band bass players had used conventional microphones as pickups for years without altering their playing styles. Some recent variations of the double bass have been fitted with pickups like an electric guitar's and are designed exclusively for use with electric amplification.

Double bass bow

There are two kinds of bows used in double bass playing: German and French. They are different in both design and playing technique. The french bow is a heavier version of the bow used by the modern violin family, and held in the same way, with the palm facing down, the fingers resting over the top of the stick and the thumb grasping the frog. The german bow has a much larger frog and is held with the palm angled upwards, as used for the upright members of the viol family.

Bass tuning

The bass has usually 4 strings tuned (lowest to highest) E, A, D, G. The strings are made of either nylon or cat gut (traditionally) or metal-wrapped synthetic or nylon. Commonly used are flat-wrapped metal strings.

Some basses have 5 strings; the additional string may be either an extra high string (tuned to C) or an extra low string tuned to B. Such basses are larger than usual, somewhat harder to play, and rare.

Many four-string basses have a 'C extension' which extends the lowest string down as far as low C, a note an octave below the lowest note on the cello. This is invaluable in classical music, because the bass often doesn't have a separately written part but is told to play the cello part an octave lower, a practice known as 'doubling'. It is this that gives the double bass its name.