Spectrum, a new loft-style contemporary-classical venue on the LES, hosts a three-day series devoted to the connections between progressive rock and classical music—a link that should be obvious to anyone who knows their Emerson, Lake & Palmer. Friday's bill features artists performing on the guitar relative known as the Chapman Stick, while the Saturday and Sunday programs showcase a potpourri of composers and ensembles. See spectrumnyx.org for a detailed lineup.