Stephen Powell as Sweeney Todd and Phyllis Pancella as Mrs. Lovett in Virginia Opera's production of “Sweeney Todd.” (Lucid Frame Productions for Virginia Opera)

Among opera companies, putting on musicals is all the rage. There are, the companies assure us, plenty of artistic reasons to do it: Musicals are the contemporary equivalent of opera, or musicals are a historical successor to opera that opera houses can present in a historically accurate (which is to say, unamplified) manner. The bottom line, though, is that presenting musicals is a way to sell tickets and reach a new audience.

That, at least, is the theory. But finding that new audience takes more than simply putting a musical onstage and trusting people will come — as the Virginia Opera has found out. The company opened its 40th season with Stephen Sondheim’s “Sweeney Todd,” which came to George Mason University (the last of its three venues) on Saturday night. “Sweeney Todd” is one of the strongest works of musical theater written in the latter half of the 20th century. It’s better put together and tighter than any contemporary American opera I’ve seen from the same period, it’s musically sophisticated, and each time I see it, I find new things to admire. But the new audience stayed away in droves; Saturday night’s crowd was one of the smallest I’ve seen for a Virginia Opera production. (Admittedly, attendance was down for last season’s “Falstaff” as well, so the problem may not be just the repertoire.)

Here’s the real challenge with musicals: You risk alienating your existing audience without finding other ticket buyers to take their place. Which is, in the case of this “Sweeney Todd” in particular, a real shame, because the evening’s strength lay in some impressive vocal performances — by opera singers.

“Sweeney Todd” is a bit like “Carmen”: a work that shocked the audience at its premiere, and loses some of its shock value as it mellows into a classic. Familiarity breeds acceptance, even of the idea that a barber kills his customers and that his sidekick, Mrs. Lovett, bakes them into pies. And Ron Daniels’s economizing production, which involved a few pieces of scenery on an empty stage and some willing suspension of disbelief on the part of the audience, didn’t especially build up the drama. The music, though, like that in “Carmen,” remains powerfully effective and evocative.

If only it were allowed to stand on its own merits. I suppose you can make a case for the necessity of amplification in a work that includes spoken dialogue; and I suppose you could further argue that one thing that hampers productions of “Carmen” (which includes even more spoken dialogue, in the original) is the slightly stilted, heightened delivery of the spoken dialogue so that it can be heard across the foot lights (although trained Shakespearean actors have long mastered this feat). But the tinny, misdirected sound of even a decent sound system, and the way it levels out the peaks and valleys and individual timbres of singers’ voices, is, to me, a buzzkill.

Yet many of Saturday’s singers were able to transcend this handicap, starting with the baritone who played the title role, Stephen Powell. Much is written about opera singers and acting, and whether they can or can’t act, and whether, if they can do it, they can really sing: Powell is one of the rare birds who truly, and excellently, does both. His voice is powerful and dark; his spoken delivery was less stilted than I’ve heard from some Broadway actors in the role. And I’ve never seen Todd done better. He was joined by the Mrs. Lovett of Phyllis Pancella, another singer better known for Bach than Broadway but who seemed here to the manner born; and both were equaled by the veteran Jake Gardner, who as Judge Turpin created a rounded and richly sung portrayal of a sleazy elderly villain (complete with the uncomfortable self-flagellation aria, which is so hard to pull off that it’s often cut).

It was a long evening, despite these three great performances and some other strong showings, notably baritone André Chiang — currently in the company’s young-artist program — as the naive, young sailor Anthony, and the chorus exerting itself nobly if slightly ineffectively as the lunatics breaking out of the asylum. But that was partly because of the stasis of Daniels’s staging, and partly because of what one might term the “operatization” of the piece, the smoothing over of its rough edges with what you could term “the ‘Carmen’ effect.” The company’s season seems to be suffering a bit from this effect with chestnuts of various ilks: “H.M.S. Pinafore,” “La Traviata” and, finally, “Salome” as the most risqué and least ­audience-friendly entry. You can’t wholly criticize a formula that brings such good singing to the opera stage, and yet it isn’t exactly a season to inflame anyone’s heart — or, evidently and alas, to sell tickets.

The Virginia Opera’s season continues with “H.M.S. Pinafore,” which will come to George Mason University on Dec. 5 and 6.