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I hadn’t fully expected what I heard at the 9:30 Club last week. I’d listened to the records, but I hadn’t recognized that layered beneath choirs and keyboards and horns and backward drum loops was a sound, immense and pure, that I’d imagined—but only imagined—for years. But there I was, deep beneath its surface, flooded with it, soaking it in.

What sent me diving into the mystic was a stunner of an 11-song set by Iceland’s most welcome musical export since Björk, Sigur Rós. What I’d been craving was a broad, shimmering roar, slow in blooming and long in dying, with grainy fundamentals and glassy overtones—a sound that fills up a room then overflows the top of it. I wasn’t sure I’d ever find it.

Organic at its heart, the sound would rise from vibrating strings, and it would require mechanical heft. (An EBow wouldn’t pass muster.) What I envisioned as its source was a cross between a dense plank of a solid-body guitar—a Gibson product, say—and an SSP. (The little boys will understand—or at least those who were little boys in the early ’70s, when Kenner, banking on the dragstrip fever of the day, introduced a line of toy cars that gained their guidance and traction from a rubber-tired flywheel revved by a rip-cord-like strand of toothed plastic called a “T-Stick.” In 1972, the SSP roster introduced a new wrinkle in aggressive playground tech. Every 7-year-old could grasp the mighty significance of “Sonic Sound.”)

What actually produced the long-sought tones—a bowed guitar—is of a hoarier vintage. The idea of dragging horsehair across something with frets, strung E-A-D-G-B-E, goes back at least to the early 1820s, when Johann Georg Staufer of Vienna invented what later came to be known as the “arpeggione.” In 1824, Schubert composed his famous sonata for the instrument; today, it is performed by nimble virtuosos on cello or viola, the arpeggione having been deemed obsolete. In the mid-’60s, the idea of such an instrument took root in rock, albeit as a makeshift. Eddie Phillips, of the Creation, and Jimmy Page, soon to be of the Yardbirds, both applied bows to their standard electric guitars. But neither appears to have considered his bow work more than a novelty, useful in Phillips’ case for spraying salacious noises over conventionally structured pop songs, in Page’s for prop effect on echo-drenched solos whose strongest parts show him continuing to think like a plectrist. For much of his seven-minute arco contribution to The Song Remains the Same’s take on “Dazed and Confused,” he might as well have been flogging his Les Paul with a hairy stick. You may understand why I was blindsided by a more felicitous deployment of the bowed guitar.

The arpeggione was so named for its facilitation of arpeggios; it wasn’t made for carving slabs of sound or, given the low curvature of its fret board, playing much louder than piano. (There are contemporary electric arpeggiones, which pop up occasionally in New Age and new-music circles, but their makers still counsel against beefy chords.) The almost completely flat fretboards of standard electric guitars, on the other hand, lend themselves to different sounds; bowed arpeggiation is all but ruled out. And unless melodies are coaxed from the outside strings or dissonant squawking is desired, it would behoove the player to understand that the bowed guitar is built for slow, sonorous, sustained chords that span all six strings.

And that’s what I heard from Sigur Rós frontman Jón Thór Birgisson. Jónsi, as he’s called, opened the third number, “N«y Batterí,” with a single bowed chord. It started in low and grew slowly, unfolding into the cavernous space it built for itself, before the band came in to undergird it and Jónsi’s falsetto joined it up in the rafters. Rather than force the instrument to fit the song, Jónsi has structured his band’s music around his phantom guitar and his equally unearthly vocals.

On earlier tours, Sigur Rós has been joined by a string quartet and Steindór Andersen, a singer of the medieval Icelandic verses called rimur with whom the band has recorded a beautiful limited-edition EP. This time out, however, the foursome was on its own, and the density of its recorded sound unexpectedly suffered little in translation. Though the band spends so much time in the studio that it has decided to build one of its own, its songs don’t require large-group treatments or prerecorded samples to stand up to live performance. Their essence—lyrical, trancelike, disembodied, collapsing time as only the most thoroughly conceived long songs ever do—actually benefited from the clarity of four-piece arrangements. Kjartan Sveinsson, whose keyboards run a close second in textural importance to Jónsi’s guitar-fiddling, also filled in on flute and second guitar. Though the rhythm section, too, ventured into multi-instrumentalism, Georg Holm generally provided the ineffable soundscapes their mnemonic bass lines with such restraint that he didn’t need to remove the pickup cover from his Fender Jazz Bass. And Orri Páll Dy«rason proved to be the band’s secret weapon, unspooling carefully colored drum patterns whether brushing around the beat or pounding home the climactic “Popplagith,” an unreleased song that is an online-bootleg favorite.

Besides “N«y Batterí,” only two other officially released songs were played, “Olsen Olsen” and “Svefn-G-Englar,” which got the only big recognition cheer of the night. It was also the only tune on which Jónsi lost his way, drifting off pitch on the stratospheric vocal hook (the loud screech-along from the crowd couldn’t have helped)—though he redeemed himself with the snazzy trick of singing directly into his pickups. On the whole, the new material, some of which will likely appear on the band’s major-label debut, due sometime next year from MCA, is sparer and more repetitious than the older songs, though that may change once it is fleshed out in the studio.

The verdict on Sigur Rós divides along party lines. Advocates claim that the boys are revolutionaries who will remake music in their own image—a mantle the group claims for itself. Doubters (not exactly haters; no one seems to despise Sigur Rós) point to a bevy of bands plowing the same turf, Spiritualized, Godspeed You Black Emperor!, and Mogwai among them.

Each side suffers under the same aesthetic fallacy—that anything good must be truly groundbreaking. What distinguishes Sigur Rós is that it brings taste, talent, maturity (however precocious), and rock-solid musical thinking to a field that has often gone wanting for at least one of the above. Quasi-symphonic art rock colored with the occasional folkism and supporting keening vocals is by no means a new genre, but you don’t need to dredge up your old copy of Renaissance’s Live at Carnegie Hall to know how easy it is for things to go horribly, horribly wrong.

For all its naked daring, Sigur Rós not only doesn’t embarrass itself but also shows up even the hippest of competition. Heard in light of the band’s most recent long-player, Agætis Byrjun, released in Iceland in 1999 and reissued elsewhere since, the new Spiritualized record, Let It Come Down, finds Mr. Spaceman to have rounded the inevitable junkie corner from charmer to bore, his squared-off, chunky melodies woefully at odds with the intended sweep of his arrangements, his “gospel” leanings increasingly ill-fitting and ersatz. The redoubtable Godspeed holds up much better, but unlike its leaner, more focused live shows, the blanker portions of its albums exhaust even the band’s staunchest fans. And the braggarts in Mogwai are a mouthy bunch to have stayed asleep at the wheel for so long; it’s always a surprise that such lively lads make such tedious records.

As is the case with many art-rock bands, lyrics may be Sigur Rós’ Achilles’ heel, but I don’t know and don’t intend to find out right now, lest I be looking the gift horse of unintelligibility in the mouth. That they’re in Icelandic functions as a home-field advantage the band can carry with it wherever it goes. Away, it works as a barrier to keep Jónsi’s particular language from stomping all over the band’s universal kind. Back home, Sigur Rós caters to a nation of roughly a quarter-million souls who love to root for the local boys. And that’s when Jónsi actually sings in Icelandic; other times, especially on the new songs, he sings gibberish. Once rumored to be the private language of Hopelandic, the nonsense has since been confessed to the New York Times to be just that.

The band’s wordless communication is an heir to what art historian Robert Rosenblum has identified as the Northern Romantic tradition. The product of physical geography, personal temperament, and the history of a culture rather than that of any specific artistic métier, the Northern Romantic lineage, which runs from Friedrich to Rothko through such figures as Munch, Hodler, and Klee, contains works, Rosenblum writes, that “seek the sacred in a modern world of the secular” and create arenas “in which spirit would triumph over matter.” It was impossible to watch Jónsi, singing as if his voice would break free of his body, his shadow cast sharply against the movie screen behind him, and not picture the signature image of Rosenblum’s argument: Friedrich’s monk, pinioned to the intersection of land, sea, and sky. Behind the singer—again, thoroughly precedented but paragons of their genre, in this case the concert-backdrop video—were indistinct shots of figures against voids, slow-motion birds, and children at play, making intuitive sense of Rosenblum’s linkages of the pastoral and the apocalyptic and the childlike and the natural.

If anything about Sigur Rós nears being revolutionary, it is its leave-taking, though that, too, owes a debt to tradition, in this case that of the concert hall. Shunning the combination of false modesty and crass calculation that characterizes the usual rock encore, the band retreated from the stage after playing a precisely planned set during which it took virtually no notice of its demonstrative audience. When the crowd, acting more out of habit than of need, demanded more, the four bandmates returned, stood at center stage, linked arms around one another’s waists, and executed a formal bow. Two more curtain calls later, they had nothing else to offer. Nothing was required. CP