Low, Royal Festival Hall, London

You don't go to the Royal Festival Hall to enjoy a band.

You don't go to the Royal Festival Hall to enjoy a band. Excitement feels alien amid its velvet-tempered brutalism, intensity is hard to build in its concrete caverns, and gigs have to end no later than 10.45pm, by which time the bar is closed. It's hardly rock'n'roll. But then, until a year ago neither were Low.

The trio have spent more than a decade releasing roughly one album a year of super-slow-mo minimalist melancholia. From Duluth, Minnesota, they have built a big critical reputation and a small but loyal following. Then, earlier this year, something extraordinary happened. They released The Great Destroyer, an album that rocked, that was properly loud, and that you could tap your feet to without having the chance to tie your shoelaces between beats. It had rave reviews.

Despite their new, bigger sound, Low are physically dwarfed by the RFH stage. They huddle uncommunicatively downstage in a pool of light, hemmed in by their amplifiers. Alan Sparhawk slashes overdriven chords out of his custom Telecaster and sings like early Michael Stipe. Zak Sally, on bass, has his back to the audience for the first few songs, and Mimi Parker, all in black, and with long curly hair, is almost invisible as she stands behind her very basic drum kit. There's no mistaking her when she sings, though, her voice being one of the two beauties of Low's music. Her effortless harmonies give the songs a transcendental quality, her counterpoints seeming sometimes to become almost one with Sparhawk's intense lead lines, their phrasing fitting each other's perfectly.

The beautiful songs are the band's other great asset. There are moments when you feel yourself willing the tempo to speed up to give the gorgeous tunes a chance to connect with a more general audience. Perhaps that's the point of The Great Destroyer. Its opening track is second up, and it feels like a statement of intent. "Tonight you will be mine;/ Tonight the monkey dies," Sparhawk snarls as Parker beats an insistent rhythm on her floor-tom, snare hissing periodically like the valve on a pressure cooker at its limit. If this is the noise of a band shaking the monkey of slow-core from their back, then "California", the next track on the album and the current single, is that of a band freed: it's a joyous jangle of a cruising anthem.

Unfortunately, the mood it sets doesn't last. Older, slower, quieter songs are mixed with the new, and a couple of numbers later, the reverent atmosphere is exemplified by the man in front complaining about me muttering a query to my companion. By contrast, Sparhawk is slowly loosening up, talking to the audience, and claiming Low have never played to so many people. They close their set with "When I Go Deaf", a gloriously long and loud celebration of overdriven electric guitar from the new album. But they encore with a quieter obscurity: the "old" Low closing a gig where the "new" Low have been the revelation.