Instrumental rock works best when it’s extreme. It doesn’t matter so much whether the group in question is impatient (Naked City) or gigantic (Godspeed You Black Emperor!) or simply reductionist (Tortoise)—it just requires some kind of sensationalism to fill the lyric void. In the case of drum-free L.A. duo Sunn 0))), aesthetic success lies in excessive slowness. Initially inspired by slothful Sub Pop band Earth, Greg Anderson and Stephen O’Malley create what is best described as ambient metal. On the band’s fourth long-player, White 1, album-closing “A Shaving of the Horn That Speared You” moves along glacially—distorted guitars rising and submerging repeatedly over its quarter-hour instrumental drone. Other tracks, however, find Anderson and O’Malley adding guest vocalists on top of the guitar crawl. On disc-opener “My Wall,” Julian “Krautrock Sampler” Cope recites his semi-epic poem about Vikings and superphalli and, well, Sunn 0))): “Play your gloom ax Stephen O’Malley/Sub-bass ringing the sides of the valley/Sub-bass climbing up each last ditch and coomb/Greg Anderson, purveyor of sonic doom.” In less time than it would take to pulverize a copy of Saint Julian, Cope has justified his entire existence. It’s that good. And Sunn 0))) doesn’t fare too badly, either, incrementally expanding its sound while sustaining the spirit of slack-stringed buzz. Foxy Norwegian chanteuse Runhild Gammelsaeter shows up next, contributing the disc’s other vocal on “The Gates of Ballard.” Gammelsaeter, who played with the Sunn 0))) boys in Thorr’s Hammer, creates a voice analog for Anderson and O’Malley’s mantralike instrumental hum: Burring in her native tongue, the singer evokes more frosty, foresty atmospherics than a bag of holding full of black-metal CDs. Well-conceived vocal contributions aside (they take up about 15 minutes of this hourlong disc), this is largely an instrumental affair. As such, it works in all the right ways, signifying the extent of rock with only foreboding fingers and a wall of amps.—Brent Burton