With audiences slowly disappearing 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 in week 13 (Aug. 20-26) 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 closing dates. Otherwise, most individual productions were down. Few dips were major, but despite the addition of 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 Aug. 26, only upticked slightly, but Brit farce “One Man, Two Guvnors” ($746,407), closing Sept. 2, was up by 13%, or close to $90,000. “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 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%, 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 as school starts, slid 12% .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 18 musicals grossed $16,654,636 for 86.3% of the Broadway total, with attendance of 164,595 and an average paid admission of $101.19. The five plays grossed $2,648,304 for 13.7% of the Broadway total, with attendance of 32,402 and an average paid admission of $81.73.