![By John and Alan Lomax Collection [Public domain or Public domain], via Wikimedia Commons](http://commons.wikimedia.org/wiki/File:Blind_Willie_McTell_LOC.jpg "Blind Willie McTell, with 12-string guitar, hotel room, Atlanta, Georgia.")
Another innovation relating to increased volume was the 12-string guitar. The use of double courses of strings to increase volume is quite old. Because Renaissance guitars and mandolins had used this concept it is perhaps is wrong to say it is truly an innovation. But the development of the modern 12-string guitar seems to me significant because of its role in early blues.
Wikipedia and other sources suggest two possible influences for the modern 12-string. One is it evolved from Mexican 11-stringed instruments. The other is that Italian luthiers evolved it from their knowledge of mandolins. What we know is that by the beginning of the 20th Century there were inexpensive 12 string guitars available and that Huddie Ledbetter purchased a Stella 12 string guitar in 1912.
In addition to Leadbelly, Blind Willie McTell and Barbecue Bob were early bluesman who took advantage of the extra volume of the 12-string guitar.
