Routinely cited as an essential entry among the very best rock albums, The Who's Quadrophenia will sound a little different this weekend at Tanglewood in Lenox, Mass. Pete Townshend, joined by punk legend Billy Idol and the opera star Alfie Boe, will present Classic Quadrophenia on Saturday night at 8. The Who's principal songwriter since the band's founding in 1964, Townshend tells the story of mods, rockers, alienation and youthful longing in the rock opera released in 1973. At this date, they'll be joined by Keith Lockhart and the Boston Pops. Townshend is performing Classic Quadrophenia at a handful of concerts this summer.