Massive Attack emerged, and made the stage look small: The two singers appear cramped by the turntables, synthesizers and drums. Calvin Tsingh’s voice is dramatic and beautiful. The band dips into the slowest mutations of dance music: hip-hop, reggae, techno. They straddle the line between emotional heat and coldness, never giving in to either. This is the most pensive dance music ever recorded.The packed house, a poor vocal mix and the lack of ventilation created conditions no fan should be forced to suffer. Legion Hall has emerged as a decent enough venue over the last several months, but this show made the generally unbearable Palladium seem comfortable.