Editing Twelve-string guitar (section)

==Design==
The strings are placed in [[Course (music)|courses]] of two strings each that are usually played together. The two strings in each of the lower four courses are normally tuned an [[octave]] apart, while each pair of strings in the top two courses are tuned in [[unison]]. The strings are generally arranged such that the higher string of each pair is struck first on a downward strum. However, [[Rickenbacker]] usually reverses this arrangement on its electric 12-string guitars. The tuning of the second string in the third course (G) varies. Some players use a unison string, while most prefer the distinctive high-pitched, [[bell]]-like quality an octave string makes in this position. Another common variant is to tune the octave string in the sixth (lowest) course ''two'' octaves above the lower string, rather than one. Some players, either in search of distinctive tone or for ease of playing, remove some doubled strings. For example, removing the higher octave from the three bass courses simplifies playing running bass lines, but keeps the extra treble strings for the full strums. Some manufacturers have produced 9-string instruments based on this setup, in which either the lower three courses are singular, or the upper three courses are singular. Additionally; some players adapted more unconventional stringing: for example, [[Big Joe Williams]] used doubled strings on the 1st, 2nd and 4th courses of his guitars; at first adapted six-string instruments and into the sixties and later usually adapted 12-strings.

The extra [[tension (physics)|tension]] placed on the instrument by the doubled strings is high, and because of this additional stress on their necks and soundboards, 12-string guitars long had a reputation for warping after a few years of use. (This is less of a problem in modern instruments, built after 1970.) Until the wide spread adoption by American makers of the [[truss rod]] after WWII, 12-string guitars were frequently tuned lower than the traditional EADGBE to reduce the [[stress (mechanics)|stresses]] on the instrument. For example, Lead Belly often used a low-C tuning, but in some recordings, his tunings can be recognized as low-B and A tunings, partially due to the unusually long scale length (~26.5-27") of the particular models of guitar that he preferred in combination with the heavy strings that were commonly available (14-70).<ref>See [[Julius Lester]]/[[Pete Seeger]] The 12-String Guitar as Played by Leadbelly, Oak Publications, New York, 1965, p. 6.</ref> Some 12-string guitars have nontraditional structural supports to prevent or postpone warping, at the expense of appearance and tone.{{citation needed|date=November 2013}} To additionally reduce string tension, 12-string guitars built prior to 1970 typically had shorter necks and scale lengths than six-string guitars, which made frets more closely spaced, with some notable exceptions such as the instruments made by the Oscar Schmidt company before their bankruptcy, which usually had scale lengths of around 26.5". Their bridges, especially in acoustic guitars, had a larger reinforcement plate for the same reason, and tailpiece and floating-bridge setups were far more common than on six string instruments as another way to combat the effect of the high tension.

Advances in materials, design, and construction in such guitars made after 1970 have eliminated most of these accommodations. Contemporary 12 string guitars are commonly built to the same dimensions and scale as their six-string counterparts, albeit still usually with heavier build and bracing.<ref>In his book ''Steel-String Guitar Construction,'' artist and luthier Irving Sloane devoted a chapter to the 12-string guitar that did not mention the subsequent advances.</ref>