Eight-string multi-scale acoustic guitar by luthier Patrick Hawley of Ottawa, Ontario
An eight-string guitar is a guitar with two more strings than the usual six, or one more than the Russian guitar's seven. Eight-string guitars are less common than six and seven string guitars, but they are used by a few classical, jazz, and metal guitarists. However, eight strings is the standard for lap steel and pedal steel guitars. The eight-string guitar allows a wider range, or non-standard tunings (such as major-thirds tuning), or both.
Various non-standard guitars were made in the 19th century, including eight-string guitars played by Italians Giulio Regondi and Luigi Legnani.
In the 1940s, American lap steel guitars generally standardized with eight strings. Tuning was usually based on either the E9 chord for "Nashville" style or the C6 chord for jazz configurations.
Seven-string guitars are needed for major-thirds tuning to have the E-e' range of the standard tuning. Eight-strings enabled Patt's highest string to have G♯ (equivalently A♭) for its open note. Patt purchased six-string archtophollow-body guitars that were then modified by luthiers to have wider necks, wider pickups, and eight strings. Patt's Gibson ES-150 was modified by Vincent "Jimmy" DiSerio circa 1965. Luthier Saul Koll modified a sequence of guitars: a 1938 Gibson Cromwell, a Sears Silvertone, a circa 1922 Mango archtop, a 1951 Gibson L-50, and a 1932 Epiphone Broadway; for Koll's modifications, custom pick-ups accommodated Patt's wide necks and high G♯ (equivalently A♭); custom pick-ups were manufactured by Seymour Duncan and by Bill Lawrence.
The solid-body eight string guitar is also used in many modern bands today. The construction of a solid-body eight-string guitar is identical to seven and six-string variants. The standard tuning (from low to high, top down) is F#, B, E, A, D, G, B, E. The tuning can always be changed. Many prefer to tune the F# to a low E (the same E on a bass guitar), providing the guitar with a fuller sound by having three different E strings. By doing this, octaves and fifths are accessed easily.
Like the seven-string, the first commercially produced eight-string guitar is made by Ibanez guitars in Japan; the RG2228
The main design issue faced with an eight-string guitar is tuning stability with the lower strings. This is due to the neck being constructed too short, bridge problems such as improper intonation, uneven spacing for floating bridges, or the use of wrong string gauges. Other problems associated with tuning stability rely on proper set up of the guitar.
A point of clarity, inharmonicity is not Intonation. Pressing a string against a fret — aside from raising the string's pitch by shortening the string — also causes a slight secondary raise in pitch because pressing the string increases its tension. The bass strings on an 8 string typically require the saddle to be pulled back a bit more than the other strings to properly set the intonation. Some bridge designs accommodate this by offsetting back the 7th and 8th strings or providing a bit extra room for adjustment. Longer scale lengths require less offset for proper intonation.
Jazz guitarist Charlie Hunter is known for playing a hybrid eight-string guitar made by Ralph Novak of Novax Guitars. Five of the strings are tuned to the standard guitar's upper five (A, D, G, B, E), while three of the strings are tuned to the standard bass guitar's three lowest (E, A, D). The bass and treble sections have separate pickups and are sent to separate amplifiers. Hunter also has a ten-string guitar based on the same principle—a combination of standard six-string guitar and standard four-string bass.
One notable guitarist, Tosin Abasi (from Animals as Leaders), tunes his guitar with the low E, and utilizes all the features of the eight-string guitar. He incorporates bass guitar techniques such as string thumping made famous by Victor Wooten (which is heard mostly on "Earth Departure, An Infinite Regression"), and harp like techniques by combining sweep-picking with hybrid-picking.
Archspire - Technical death metal.
Beyond Creation - Progressive death metal on multi scale 8 string guitars.
^ Peterson (2002, p. 37): Peterson, Jonathon (Winter 2002). "Tuning in thirds: A new approach to playing leads to a new kind of guitar". American Lutherie: The Quarterly Journal of the Guild of American Luthiers (8222 South Park Avenue, Tacoma WA 98408: USA.: The Guild of American Luthiers) 72: 36–43. ISSN 1041-7176.