Like a good business, the 18th Street Singers have identified their niche and formulated a game plan and, with seven years of growth under their belts, are seeing success (they are just back from a stint at the Piccolo Spoleto Festival in South Carolina). The singers are 45 young professionals who sang in their college choruses and a cappella groups and, in a large and impersonal city, this chorus has become their community. The audience that packed the Kennedy Center’s Terrace Theater for their concert on Sunday was a lot like them (parents and older relatives excepted) — young, enthusiastic, informal and delighted with a program that moved the bar of sophistication just beyond their old glee-club favorites.

It was an odd program that began with Frank Martin’s Mass for Double Choir (a piece that is getting a lot of airing this year); it then scattered folk-song settings, Antonio Lotti’s “Crucifixus” and bucolic songs by Rheinberger and Brahms among a bunch of short, easy-listening contemporary pieces by Imogen Heap, Ola Gjeilo and Toru Takemitsu. But it was all well sung (although the Brahms “Waldesnacht” could have used a much bigger dollop of romantic imagination) and delivered with energy and commitment.

Conductor Benjamin Olinsky has a first-rate bass section to work with, high voices that produce a straight tone, and personnel committed to blend and ensemble. What the clarity of the singers’ diction exposed, however, was a tendency to let the diphthongs that worked so well in the folk songs ooze into the Latin texts, where they might make any lover of Latin shiver.

Assorted members of the chorus offered lively introductions to many of the pieces, and chorus alumni, invited to the stage to join in the singing of an old Yale arrangement of “Shenandoah,” responded in droves and were greeted with hugs and cheers.

Reinthaler is a freelance writer.