A richly curtained proscenium would have been all wrong, but the long, white, high-ceilinged room - once a fish refrigerator - was a provocative setting Sunday for the JACK Quartet's survey of the intricate, still music of the New York School. The players, ringed by listeners, played music by Morton Feldman, Earle Brown, John Cage - and Anton Webern - in the second American Sublime festival event, at the Crane Center in Northern Liberties.

The program summarized the revolutionary thought of the mid-20th century, when composers rebelled against every element of Western music. And, because Feldman, Brown, and Cage were paracletes at the altar of Webern, who removed all traces of narrative, reference, and tonal imperatives from the European tradition, his Six Bagatelles were played as a touchstone, almost as a classic.

The New York School valued music's fluidity. Scores had interchangeable pages. Players decided the order of performance so the music never sounded the same. Scores were written on graph paper, or encrypted to avoid repetition. Nuance was the music's lexicon; silence a goal. But players' virtuosity was assumed.

The JACK players, deep into the technical demands of the program's terse works, freed the power of miniature touches and implied rhythms. In the whispered brevities of Feldman's Structures and Brown's Quartet, the still details made pizzicato sound like a percussion section.

The beauty of the intimate setting let listeners see the scores on the stands, but also the violinists touching strings with the bow's hair, then the wood, then both. They could see the playing below the bridge, savor the different tunings that asked fresh ears.

Feldman's piece was played twice, to open and close the program. Its hushed, luminous touches, quick patterns, and witty arpeggios affirmed its title. There are tiny structures in there, flashes and clouds, transparencies and moments. Its atmosphere was so taut and coherent that each performance ended with listeners hushed.

Brown's String Quartet accepted as a tenet Alexander Calder's mobiles, works that, by constantly moving, are never seen the same. Brown gave his players choices within a shadowy form. The music proved expressive, mystical, superbly shaded and joined. Brown's vocabulary is enormous and his power of suggestion, with these four instruments, mesmerizing. The ensemble fits details together neatly without losing the spirit and wit that shines deep within the writing.

Cage's Quartet in Four Parts offered larger sounds and some echoes of early formal training. Nevertheless, in 1950 it must have seemed iconoclastic and baffling. In this reading it sounded a bit like an American classic, for many of its ideas have been absorbed into the language. Its quickness and refusal to suggest sentiment seemed a portrait of the composer's mocking grin.

And Webern? In this white-walled context, it sounded like old Vienna. The music's strong forms, the order of its detailed sounds and bold slashes, and the lack of repetition and reference asserted its monumentality. This was the start, its daring now part of every composer's language. The performance was touched with gratitude.