The Roman new music ensemble Nuova Consonanza returns to the American Academy in Rome for its 48th season, presenting “Festa d’Autunno 2011.” A Friday inaugural concert will feature John Cage’s String Quartet in Four Parts (1950), Steve Reich’s Different Trains (1988), and work by Ivan Fedele, performed by the Quartetto Prometeo. A Sunday all-day marathon staged throughout the Villa Aurelia will feature installations and performances of music by composers including Samuel Barber Rome Prize Fellow Sean Friar and Elliott Carter Rome Prize Fellow Lei Liang.