Kraftwerk emerges at 9:30 Club in world of their own creation

It's an odd sight, a thousand or so concertgoers in paper frames. Balding electro fanatics and their kids standing next to shaggy 20-somethings, all with 3-D lenses, glued to a big screen. Turn toward what they're looking at, and . . . still sort of odd: four balding electro fanatics in gridded spandex, standing over glowing podiums.