Vibrant, assertive new music from the Flux string quartet

Named after the absurdist Fluxus art movement of the early ‘60s, the New York-based Flux Quartet is among the more invigorating, genre-expanding entities on the string quartet scene. Founding violinist Tom Chiu and his current confederates -- violinist Conrad Harris, violist Max Mandel and cellist Dave Eggar -- play with passion, crystalline focus and sprinkles of humor.

In 2003, the quartet made a splash, even beyond modest new-music circles, by taking on Morton Feldman’s infamous String Quartet II, an ultra-spare, mind- and time-expanding six-hour work. (The Kronos Quartet performed it in the ‘80s in a brisk four-hour model but quickly swore it off.) Monday at the Los Angeles County Museum of Art, the Flux presented an altogether different new-music picture, one that teemed with assertive -- even rocking -- sounds.

Although grounded in contemporary music, the program also delved into far, fuzzily defined corners of rock and jazz. Composer and avant-rock guitarist Elliott Sharp writes intense string music, the bowed equivalent of manic guitar strumming. His two-chord, vampish “Tesalation Row� generates a gritty, sawing ensemble tone, sounding like a big surrogate distorted guitar.

Composed by a jazz artist prone to shunning categories, Ornette Coleman’s “Poets and Writers� is continually evolving, making each performance a quasi-premiere. In its scattered construction and atmosphere of pleading lyricism are traces of Coleman’s “harmolodic� notions and also of his unique violin playing, somewhere between enlightened child’s play and devoted nonconformism.

Chiu’s own “SAS� seems inspired by Coleman’s concepts; it fudges the lines between score and improvisation and is built around rising and falling ensemble energies. Michael Byron’s “Awakening at the Inn of the Birds� is minimal without being Minimalist in the classic keep-your-riffs-running way. Its seductively swaying, almost breath-like waves of action are redolent of bagpipes or circular accordion textures.

The concert’s highlight came from a 20th century “old master,� Iannis Xenakis. His 1983 “Tetras� plays with the string quartet palette while sidestepping melodic or thematic concerns or even a fixed musical language. Instead, he explores varieties of gesture and noise potential, all tightly fashioned into a form suggesting an elaborate sound sculpture and/or ritualistic event.

The Flux amply proved its mettle with this tour de force, the brightest spot in a headily vibrant evening.