For this actress: drumroll, please

If you’re thinking it’s time for a rim shot, you’re right. You see, this Jules and Jo are part of a history-museum exhibit in the distant future. Barbara, the docent who controls and narrates the exhibit, has taken it on herself to provide percussion effects: timpani rolls, cymbal crashes, the whole gamut.

“Barbara is very involved in this particular exhibit. She really helped to create it. It was quite boring, as she tells us, when she first took over,’’ says Karen MacDonald, who plays Barbara in the New England premiere of “boom’’ by Peter Sinn Nachtrieb, which starts performances Sunday at New Repertory Theatre.

“She’s made the exhibit far more interesting for everyone, because she really considers it so very important, that we must look back and see where we came from,’’ MacDonald says. “I think it’s the only thing she does in the museum, frankly. You get the feeling they like to keep her away from the rest of the museum. ‘Oh, fine, let her just do this.’ Over and over again, eight times a day this goes on.’’

Directed by Bridget Kathleen O’Leary, New Rep’s artistic associate, “boom’’ stars Zofia Gozynska as Jo and Scott Sweatt as Jules. The dark comedy is the most produced play of the 2009-10 regional theater season, according to the Theatre Communications Group.

Sound designer Matt Griffin brought MacDonald her instruments, which also included hand cymbals, cowbells, and a flexatone, which produces a wobbly, cartoony sound. A sometime drummer himself, he gave MacDonald some basic instructions, but the goal wasn’t to make her a symphony-class timpanist.

“This is Barbara’s show. I don’t want to give away too much, but she’s a self-taught woman. It works both with the script and on the practical level, in that Karen isn’t trained in this sort of music,’’ Griffin says. “I feel as long as she does whatever she does with conviction, it fits the character.

“The particular drum we have looks quite well loved or maybe abused,’’ Griffin adds with a laugh. “It’s dented, and we’re still waiting on a new head. . . . She’s hitting the side of it and the lugs. She’s really playing it wrong, but that’s sort of what we’re going for.’’

A former member of the American Repertory Theater’s acting company, MacDonald recently won acclaim for her performances as Kate in “All My Sons’’ and Mary Todd Lincoln in “A Civil War Christmas,’’ both at the Huntington Theatre Company. Her next performance will find her playing seven roles in the one-woman show “The Blonde, the Brunette and the Vengeful Redhead’’ at Merrimack Repertory Theatre.

While MacDonald was in “All My Sons,’’ she says, she made a few pilgrimages to the Museum of Fine Arts and joined docent tours by way of research.

“There’s a sort of quiet passion that some of those people have about the artwork they’re showing you and how knowledgeable they are,’’ MacDonald says. “But Barbara’s not so quiet with her passion. She’s not going to go out to her car and get a gun or anything. But it feels a little like the postal worker who’s been canned. Just a tad. She’s a little desperate. It’s very important to her to keep this job. This job from her point of view is the reason for her existence. And these two people who comprise the exhibit are extremely important to her. Jules and Jo, they’re like her children. She wants to protect them.’’

Runs through March 13, Downstage @ New Rep, Arsenal Center for the Arts, Watertown. Tickets: $25. 617-923-8487, www.newrep.org.

For the Roxbury run, sponsored by Roxbury Center for Arts at Hibernian Hall, tickets are $15: 617-849-6322, www.madison-park.org. For the Providence run, tickets are $20: 401-621-6123, www.Arttixri.com.