The Ogden Theatre isn't exactly a quiet room. On most nights, the music is loud and so is the crowd, the members of which angle for position, and cocktails, on the floor and in an upper balcony. But when the Icelandic dreamspace outfit Sigur Rós performed for a sold-out show in November, the place took on the feel of a symphonic chamber. Attendees appeared genuinely stunned by the gorgeous, whale-sound music they were hearing, as well as the accompanying film reels projected on a giant screen. Vocalist Jón Thor Birgisson wailed siren songs and led a large band through waves of blissful sound shaped by keyboards, piano, strings and guitars played with violin bows. No wonder the audience couldn't stop staring: Watching Sigur Rós's performance was like watching the Northern Lights move about the sky.