Sound designers usually draw raves for obvious effects: street traffic, flocks of chirping birds, hammer-the-walls thunder. Their background scores also set mood and period. But the sound designer’s primary job is far more crucial: how well do you hear the actors?

The Old Globe is staging Michael Hollinger’s Opus in its temporary faux–Cassius Carter playing space. Designer Lindsay Jones handles the quirks and potential dead spots, of what is essentially a large museum room, with ease. The cast, playing the members of a string quartet, can stand anywhere on Kate Edmunds’s bare, particle board-like floor and speak clearly for all to hear. Water boiling for Dutch tea in the next room has just the right whistle.

What Jones does with his other assignment is as impressive. Most sound effects are unexpected (only in hindsight does the dog’s random bark occur at the perfect moment). In Opus, you can see Jones’s coming. At various times, the quartet reaches for the two violins, viola, and cello. In the symphonic equivalent of “air guitar,” the actors fake playing them. They slide the bows with verisimilitude but don’t attempt the fingerings, say, for Beethoven’s Opus 131 (another telltale sign: there’s no rosin on the music stands). At the precise moment when the bows hit the strings — and after a while you’ll find yourself inspecting each touch for the slightest infraction — the music begins. Sights and sounds fuse.

Jones has the “performed” music emerge, it would seem, from the instruments themselves. Sometimes he moves the music from the stage to speakers behind the audience: it drifts up and then out, as if, in the case of the Beethoven, it’s headed home to heaven.

Opus moves pretty much as expected: out of backstage chaos comes an astonishing order. The all-male Lazara String Quartet, named for the fictitious Pietro Lazara, has gained an international reputation. They won a Grammy for their Bartók, have recorded almost all of Beethoven, and will perform at the White House before an estimated 15,000,000 American TV viewers. The President, a raging Philistine, wants “Hail to the Chief” and — of such stuff is Muzak made and somnolence assured — Johann Pachelbel’s Canon in D.

Six days before the command performance, the viola player, Dorian, disappears. He has Beethoven’s temperament and possibly a glimpse of the master’s genius. Dorian’s tantrums have driven the others nuts. But his complaints and proddings have honed them into a unit (when the score says “Sforzando,” he determines just how suddenly surprising it should be). Elliott, first violinist, self-appointed leader of the group (and Dorian’s ex-lover), says the viola player crossed a line.

Dorian vanishes, and the play’s double plot moves forward and backward. The best candidate for the job thus far doesn’t make music, says Elliott, “he extrudes notes.” Enter young Grace. She chose the viola, years ago, for the way it looked. In her audition, she performs far better than her résumé says she should. She joins the group and hears utopian harangues about “four equal voices” and choices built on “consensus” and losing “all awareness of who’s who and there’s just the music” — and she wonders if all the rumors about the group’s legendary bickerings, some life-threatening, are true.

The script unfolds as if written in haste. The characters are stencil-thin, and — except for a coda that’s a gratuitous lulu — the plot moves predictably toward the Big Event with few Sforzando-like surprises. At its best, Opus is about the collaborative process and how an artistic whole can be far greater than its parts (“never perfect,” wise Dorian says, “just closer”). When the characters bicker about interpreting a musical passage, they not only fill the stage with passion, they reveal themselves in detail.

If a play calls attention to an artistic collaboration, it’s hard not to inspect the production’s inner workings. The Old Globe’s Opus resists such a perusal, however. As if each character were an instrument and each scene a different tempo, director Kyle Donnelly has melded her fine ensemble cast into the fluidity of music. Each one brings more to the role than exists in the text. Jim Abele gives controlling Elliott layers of toxicity. Jeffrey M. Bender’s Alan plays second violin with a second banana’s infectious sense of humor. Mark H. Dold makes Dorian a loose cannon, locked and loaded. Former UCSD students Corey Brill and Katie Sigismund shine as Carl (the cello player whose bad news fuels the plot) and as Grace. Sigismund’s portrayal of the gifted young woman, thrust into a male fraternity and having to find her place, is so precise you’d swear she’s based it on an exact model.

The play talks a great deal about the oneness musicians can achieve. The director creates a memorable visual by showing us the quartet the moment after. They excelled. Now, strung across the stage, they look back into the fading light as if waking from a dream. They were the music — to paraphrase T.S. Eliot in Four Quartets — at least while the music lasted.

Opus, by Michael Hollinger
Old Globe Theatre, Simon Edison Centre for the Performing Arts, Balboa Park
Directed by Kyle Donnelly; cast: Jim Abele, Jeffrey M. Bender, Mark H. Dold, Corey Brill, Katie Sigismund; scenic design, Kate Edmunds; costumes, Denitsa D. Bliznakova; lighting, York Kennedy; sound, Lindsay Jones
Playing through April 26; Sunday, Tuesday, and Wednesday at 7:00 p.m.; Thursday through Saturday at 8:00 p.m. Matinee Saturday and Sunday at 2:00 p.m. 619-234-5623.