Though the inviting Naumburg Bandshell in Central Park is just over 90 years old, this summer is the 109th season of free classical music at that site. This series concludes with musicians from the prestigious and popular Chamber Music Society of Lincoln Center, playing works by Haydn, Paul Schoenfield and Carl Maria von Weber. About 900 chairs are available for seating, but many concertgoers typically fill the nearby benches and lawn.