Broadway biz deflated a bit over the week ending Aug. 20, with the majority of the 23 shows on the boards seeing dips at the box office.Still, with total sales around $15.5 million, grosses remained relatively strong before the precipitous dropoff expected to occur, as it usually does, after Labor Day. Productions that bucked the downward trend included “Martin Short: Fame Becomes Me” ($371,396), up a bit despite a heavily comped opening week; “Sweeney Todd” ($363,863), in its final weeks before a Sept. 3 closing; and “Jersey Boys” ($1,105,859), holding on to fourth place in the top 10. “Kiki & Herb: Alive on Broadway” ($117,541) played seven perfs during its opening week, indicating that even last week’s strong review in the New York Times won’t much expand the downtown duo’s aud outside its niche. Biggest drop of the week, more than $80,000, was seen by “The Drowsy Chaperone” ($885,262), while another of the spring’s offerings, “Tarzan” ($789,289), lost around $50,000 worth of ground — suggesting that both may be more vulnerable to fluctuations in overall biz than other offerings from last season, such as “The Color Purple” ($1,106,609) and “Jersey Boys.” “Dirty Rotten Scoundrels” ($444,660) fell almost $60,000, which makes the producers’ decision to shutter the show Sept. 3 look even wiser. This week, Usher starts perfs in “Chicago” ($504,719), and the Rialto is waiting to see just how much of a bump that’ll give the revival, which also will get a publicity boost this fall from its 10th anni. The 21 musicals grossed $14,648,975 for 92.3% of the Broadway total, with attendance of 164,499 at 73.7% capacity. The two plays grossed $853,163 for 5.5% of the Broadway total, with attendance of 12,140 at 82.0% capacity. Average paid admission was $89.05 for musicals, $70.28 for plays and $69.80 for all shows.