The great bard of Irish R&B is hunkering down for a three-night stand at the Fox Theater. You never know what you're going to get from a Van gig—or what mood the famously prickly singer-songsmith will turn up in—but he remains one of the least contrived performers of his generation. While Morrison's vocals might have diminished over the years, his penchant for thrilling improvisational risk remains very much intact.