Five-string bass guitar

An extended-range bass is an electric bass guitar with a wider frequency range than a standard-tuned four-string bass guitar.

One way that a bass can 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.

...
Wikipedia