After seeing the post of the 70's advertisment for Jim Jorgeson, or whoever it was with the Doulbleneck 4 and 8 string Bass, I started wondering why people use doublenecks like 12 string guitars and a 4 string Bass, is there any famous songs where the 12-string guitarist decides to play a few bass notes, I am also interested in hearing any ridiculous combinations that people have came across from any company, such as a doubleneck mandolin and seven string guitar doubleneck, etc.