One way that a bass can be considered 'extended-range' is to use a tuning machine mechanism that allows for instant re-tuning, such as the popular 'Xtenders' made by Hipshot detuners. When the player triggers the detuner, it drops the pitch of the string by a pre-set interval. A common use of detuners is to drop the low E to a low D. Detuners are more rarely used on other strings. Michael Manring uses basses with detuners on every string; this enables him to have access to a greater number of chime-like harmonics.
Another way to get an extended range is to add strings. The most common type of bass guitar with more than four strings is the five-string bass. Five-string basses often have a low-B string, extending the instrument's lower range. Less commonly, five-string instruments add a high C-string, extending the higher range. Less commonly, the six-string bass guitar is used. Most commonly, six-string basses add a low B and a high C, extending the range on the low end and the higher register, although other tunings are used. Basses have been made with seven, eight, nine, or even fifteen strings with extremely wide necks and custom pickups. These too, are considered extended-range basses.
Michael Manring's 'Hyperbass' by Zon guitars and Les Claypool's main Carl Thompson piccolo bass are both four string basses but with necks that exceed the standard 24 frets (24 being the 'standard' for most commercially available bass guitars). Les Claypool's piccolo bass has 32 frets whereas Manring's Hyper Bass is a fretless instrument (however if it were a fretted bass it too would also exceed the 24th fret).
Extended-range bass does not refer to bass guitars with double or triple courses of strings such as the eight-string bass guitar or twelve-string bass, both of which could be considered as standard four string basses but with the addition of piccolo bass strings, tuned in octaves. These strings are generally played in unison with the bass strings, thereby producing a natural chorus effect.
The Ibanez Ashula bass guitar, though having six strings, would also not be considered as an extended-range bass because the first four strings - E A D G - lie over a section of the fretboard that has frets whereas the last two strings are - D & G again - lie over a fretless part of the same fretboard.
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In 1956 Danelectro introduced their six-string bass (tuned EADGBE, an octave below a six-string guitar). Fender brought out the Fender Bass VI in 1961. In 1965 Fender introduced the first five-string bass guitar, the Fender Bass V. Pat Fairley of Marmalade changed from playing rhythm guitar to a 6-string bass in 1965/6, the band then had two bass guitarists, the other being a 4 string played by Graham Knight.
In 1975, Anthony Jackson asked Carl Thompson to build him a six-string bass guitar tuned (from low to high) BEADGC, which he called the contrabass guitar. Jackson's bass extended the range of the bass both lower and higher than a four-string. Though Jackson initially received much criticism for the new instrument, the deep sounds of the low "B" string has become a standard in many genres including metal, R&B, funk, gospel and now country.
In the late 1980s, luthier Michael Tobias made the first bass with more than six single-course strings, a custom-order seven-string bass for bassist Garry Goodman, tuned BEADGCF. In 1988, Atlanta luthier Bill Hatcher also made a seven string bass tuned EADGBEA (the lowest six strings follow standard six-string-guitar intervals - EADGBE - and the seventh string is an added fourth above). A later tuning was BEADGBE, following standard seven-string-guitar tuning (EADGBE plus a low B).
Since that time, luthiers have been adding strings to their custom basses. In 1995, luthier Bill Conklin made a nine-string bass for Bill "Buddha" Dickens and in 1999 luthier Alfonso Iturra made an eight-string bass for Igor Saavedra. Subsequently, other luthiers built instruments with up to twelve strings. Custom bass builders have added both lower strings (such as F# and C#) and higher strings (such as F and B?) to the six-string bass guitar.
Construction of basses with more than seven strings has largely been the realm of boutique luthiers, with the exception of several production-run models including Galveston seven- and eight-string basses and Conklin Groove-Tools line of seven-string basses.
Some extended-range basses are built to a player's specific preferences, including variation in scale length, appearance, and electronics. Due to the fact that the scale length of a typical bass guitar (34" or 35") produces excessive tension on the highest strings of extended-range basses, a builder may use slanted or fanned frets to achieve a variable-scale instrument (such as the instruments by Novax Guitars), in part reducing likelihood of these strings breaking.
Usually, extended-range basses are tuned in fourths. The most common methods of tuning a seven-string bass are F# to C or B to F; an eight-string to F# to F; a nine-string to F# to B?; a ten-string to C# to B? or F# to Eb; an eleven-string to C# to E? or F# to A?; and a twelve-string to C# to ?A? or B to G?. Five string basses are normally tuned B-E-A-D-G, i.e. they have a lower B-string in addition to the four strings of a normal bass guitar. Jazz bassist Steve Swallow tunes his five string bass E-A-D-G-C, i.e. it has a high C-string instead of the low B-string.
The techniques used to play the extended-range bass are virtually identical to those used for standard 4-string basses, including pizzicato (finger plucking) or use of a plectrum (a.k.a. 'pick'), the slap and pop technique and tapping.
The upper strings of an extended-range bass allow bassists to adopt playing styles of the electric guitar. One such style is the practice of "comping", or playing a rhythmic chordal accompaniment to an improvised lead. The increased polyphony of extended-range basses allows for voicings of five or more notes, as well as wider voicings such as "drop 3", "drop 2+4" and "spreads." Walking a bassline and comping at the same time is also possible, which is useful in jazz combos lacking a chordal instrument, or in accompaniment of a chordal instrument during their lead portion. Two bassists notable for adopting this style are Todd Johnson and Oteil Burbridge.
The added strings of the extended-range bass compound the muting problems that many bassists encounter. Because of sympathetic vibration, a plucked note makes that same note (and its octaves) sound on all strings that are unmuted. Extended-range bassists often turn to hairbands or advancing muting techniques, including the "floating thumb" technique (allowing the thumb of the plucking hand to mute lower strings), to achieve a good sound.
The role that the extended-range bass plays in music is still largely a matter of situation and personal preference. Many extended-range bassists play the bass part in bands, but many also perform their instrument in a solo setting, often using advanced techniques such as two-handed tapping or chording. Still, others are exploring the extended-range bass's potential through the art of looping by layering complex bass parts, melodies, and harmonies on top of each other.