The old rule of the music biz used to be that record sales drive concert sales, and vice versa.
But it’s tough these days to find an act that can deliver robust album sales and move concert tickets.
Apart from Justin Timberlake — whose “FutureSex/LoveSounds” is the seventh highest selling album of the year (998,000 copies) and whose tour is No. 2 on the concert chart ($42.3 million gross) — few acts placed prominently on both mid-year tallies.
Concert promoters will say it’s nothing new, but for more than a decade they’ve fretted about the paucity of artists  with staying power as arena or even stadium acts.