ZZ Top is a rare band for the following achievements: They attract a huge audience playing songs undistinguishable from one another. They went techno during the 80s yet the fans still love them. AC/DC is known for No.1, and Kiss for No.2. But do we know a band that did both?Doubleback, soundtrack of Back to the Future III, is aptly titled: if you go back and come back again (double back), everything remains the same. The video says it loud: sunglasses, girls in hot pants, and synthesized guitar sound. The same old ZZ Top. Staple song: Tush / Sleeping Bag (If you picked the latter, you’re old.)P.S. Frank Beard, the drummer, is the only ZZ Top with no beard.