As its two albums and EP have proven, Gastr del Sol doesn’t rely heavily on Western notions of music: Harmony, melody, and structure give way to unresolved arpeggios, open-ended drones, and brutal riffs, at times within the same composition. Serial composers who use patterned but arbitrarily placed scales without regard to tonality are perhaps the closest relatives to the Chicago duo’s classical rock. The Crownhate Ruin and the Sorts open at 9:30 p.m. at the Black Cat, 1831 14th St. NW. $6. (202) 667-7960. (Christopher Porter)