Ticket sales for the Chicago Symphony’s summer season at Ravinia have been down for the better part of a decade now, and while the numbers certainly don’t indicate a crisis, they might point to a general malaise. “The apparent defection of a segment of Ravinia’s core audience over the last 15 years strikes at the artistic heart of America’s oldest music festival even as it tests the goodwill and durability that have marked the Chicago Symphony’s long relationship with Ravinia. Business partners during the summer who lead largely independent lives during the rest of the year, Ravinia and the CSO now find themselves in circumstances that call for something they haven’t much done before, cooperative problem-solving.”