MUSIC REVIEW : Emerson Quartet Plays at Performing Arts Center : The concert gathers steam as it progresses--beginning with Mozart, ending with late Beethoven--and doesn’t let up until the last note of the encore.

One can tell a lot about a music ensemble just from the kind of audience it attracts.

The gathering Tuesday at the Emerson String Quartet’s concert at the Orange County Performing Arts Center seemed like a crowd of aficionados, bandying about names of contemporary composers, tossing off opus numbers. One person was actually looking forward to the prospect of hearing a work by Elliott Carter, even before knowing it would be his relatively mild Elegy.

That the Emerson--violinists Eugene Drucker and Philip Setzer, violist Lawrence Dutton, cellist David Finckel--matched its audience’s level of sophistication is perhaps no news: It does that consistently. That the players accomplished it with such a technically demanding, listener-challenging program only seems characteristic.

This concert in the 299-seat Founders Hall gathered steam as it progressed--beginning with Mozart, ending with late Beethoven, American music at its center--and didn’t let up until the last note of the encore.

In Beethoven’s Opus 127, the Emersons revealed a command of ensemble techniques that allowed the music to flow effortlessly while it spoke expressively, with spacious feeling yet driving intent. The music could rise to heights of intensity yet never seemed pressed. Dynamic contrasts proved large and sudden but so well balanced and planned that they never seemed laid on to impress.

In lesser hands the massive Adagio can become a monotonous journey; the Emersons brought constantly new and vaster prospects into view, subtly holding back harmonic changes then comfortably settling into them. They captured the full measure of obsessiveness in the final movements with athletic aggression and a sound reaching symphonic amplitude.

With Drucker playing lead--his tone is leaner than Setzer’s--the other players occasionally overpowered him. More problematic, however, was the constant electrical hum from the room’s overhead lighting. Otherwise, a magnificent performance.

The group opened, a tad shakily at first, with a richly melodious and outgoing reading of Mozart’s “Dissonant” Quartet, K. 465. Unlike other recent visitors, namely the Fresk and Talich Quartets, the Emerson took into account the many facets of Mozart’s music.

Carter’s brief Elegy followed, unwinding with luminous melodic invention; and then Samuel Barber’s partially neglected String Quartet (the middle movement is the much-played Adagio), its bustling, abruptly contrasting outer movements delivered with bravura, its slow movement seething then blooming warmly.

In encore the ensemble whipped at lightning speed with mounting enthusiasm through the finale of Beethoven’s Opus 59, No. 3.