With Broadway audiences slowly waning in the final weeks of summer, it seems like the only way for producers to get a show’s sales to pick up is to announce its close.That was the case last week, anyway, when the handful of titles to see B.O. improve vs. the prior frame — “Sister Act,” “One Man, Two Guvnors,” “The Best Man,” “Clybourne Park” — were all facing imminent shuttering dates. Otherwise, most individual productions were down last week. Few dips were major, but despite the addition of new tuner “Chaplin,” the overall effect was a dip in both B.O. cume and attendance. At least the soon-to-close shows could benefit from last-minute biz. “Sister Act” ($814,882), which shuttered Sunday, only upticked slightly, but Brit farce “One Man, Two Guvnors” ($746,407), closing Sept. 2, was up by 13%, or close to $90,000. Winner of the top play trophy “Clybourne Park” ($420,369), also closing Sept. 2, was up 11% (or $40,000), and “The Best Man” ($575,811), set to exit Sept. 9, stepped up a bit last week too. Also adding to the pot were the first eight previews of “Chaplin” ($356,882) in a so-so start that’s unsurprising for an untested title launching perfs in the last weeks of summer. It remains to be seen whether the Little Tramp bio-tuner, which played to an audience capacity of 72% last week, can parlay word of mouth into sales momentum. Most notable decline of the frame was logged at “Nice Work If You Can Get It” ($502,446), off 33% (or close to $250,000) thanks to the weeklong vacation of topliner Matthew Broderick. “Mary Poppins” ($836,240), which thrives on the summertime tide of family-oriented tourists now beginning to dry up for the season, slid 12% (or $115,000), and “Peter and the Starcatcher” ($368,042) was down 14%. Overall Broadway sales slipped by $1.6 million to $19.3 million for 23 shows on the boards, with attendance falling about 6% to 196,997. The soon-to-close productions may continue to sees B.O. rise, but in general the week ahead could bring further slowdowns prior to the more precipitous plummet that traditionally hits Broadway after Labor Day.