It was an unusually hot February day to sit outside and play music for more than an hour, but that’s exactly what the ensemble did. As bewildered foot traffic and motorists passed by on Grand Avenue, the ensemble played Terry Riley’s hypnotic “In C.” They played the kind of instruments you’d expect to see in concert halls; instead of an orchestral pit or heavy curtains, though, their stringed instruments and sheet music were surrounded by chain-link fences and asphalt.