I found this herehttp://bluegrassnation.org/link_type/the-difference-between-bluegrass-old-time-and-celtic-bands-now-finally-explained/ Bass A Celtic band never has a bass, while a Bluegrass band always has a bass. An old, Old Time band doesn’t have a bass, but new time Old Time bands seem to need one for reasons that are unclear. A Bluegrass bass starts playing with the band on the first note. An Old Time bass, if present, starts sometime after the rest of the band has run through the tune once depending on the player’s blood alcohol content. A Bluegrass bass is polished and shiny. An Old Time bass is often used as yard furniture.