Nashville is a city filled with professional musicians and listeners, so it makes sense that amateurs — music lovers who lack the vocabulary insiders use to describe it — should get a chance to see and hear how music works. A journalist and musician whose work includes the 2007 book Air Castle of the South, Craig Havighurst has assembled a one-man show titled “String Theory,” which bridges musical genres in an effort to remove some of the cobwebs clinging to musical production. Using recorded sound, visuals and his own playing, Havighurst makes a case for the kind of amateurism that recognizes how the methods of serious music can inform the humblest tunes. Tonight’s show is part of Nashville Fringe Festival, which gives local artists the chance to strut their stuff. Wendy Walker Deason and the Scene’s own Jack Silverman will present the Fringe Festival’s Legends Awards to Grimey’s owners Mike Grimes and Doyle Davis.