With the wisdom of hindsight, it makes perfect sense that elegantly balanced chamber ensembles like the string quartet or the woodwind quintet sprouted in the 19th century, and that the 20th century gave us more chaotically varied mixed-timbre groups and the high-energy assertiveness of percussion ensembles. A new recording by the Baltimore-based Icarus Quartet suggests that the 21st century might see a refinement of the mixed-timbre approach, with instruments that typically inhabit distinct sound worlds creating a common language.