If ever there were a sign that the current North American orchestral “crisis” does not signal the inevitable demise of the form, the Nashville Symphony is it. As other mid-sized orchestras around the country file for bankruptcy, issue general panic alerts, and beg the public for short-term emergency cash infusions, Nashville has quietly and competently gone about raising $100 million of the $120 million it needs to build a new concert hall in the city’s vibrant downtown. Construction begins this week, and the hall, which will seat 1,900 and be owned by the orchestra, is expected to be completed by the beginning of the 2006-07 season.