It's funny to think an act originally from California could sound so swampy and Southern by today's standards, but the Doobie Brothers were very much of their time. It was the early '70s, and these happily hairy guys seemed to embody everything about a sort of just-posthippie, freewheeling, motorcycle-on-a-long-road sort of aesthetic. "Listen to the Music," one of the band's biggest hits, is all of that, plus a dose of booze and maybe some pharmaceuticals, in feel-good song form. The Doobies rode the '70s out hard, disbanding in the early '80s. Still, that lasted only a few years. From about 1987 to today, the band has played more or less continuously. With that long a lifespan, though, it's natural that the lineup has changed time and time again due to disagreements and even deaths. The current iteration, which hits Hard Rock Live on Friday, features original members Tom Johnston and Patrick Simmons on guitars, vocals, and various other instruments, with a large cast of assorted supporting players.