Jonsi (left) of Sigur Ros performs at the Patriot Center in Fairfax, Va. on the opening date of their 2013 North American tour. (Kyle Gustafson/For The Washington Post)

After Sigur Ros performed at Lincoln Theatre in 2002, I asked a friend who had attended for his opinion of the concert. “I fell asleep,” he said. “It was great.”

At the Patriot Center on Sunday night, the Icelandic band proved that it is still capable of striking a balance between bombast, bliss and boredom.

Formed during the mid-’90s, Sigur Ros found an international audience in the early ’00s following the release of its second album, “Agaetis Byrjun.” The music blended the theatricality of progressive rock with the soothing tones of ambient music.

Lead singer Jon Por Birgisson, who goes by Jonsi, crooned nonsense syllables in an alien-sounding falsetto and kicked up walls of white noise by playing his guitar with a violin bow. The band shared some turf with post-rock outfits such as Godspeed You! Black Emperor and Mogwai — groups that used rock-band instrumentation to create compositions that echoed modern composers such as Glenn Branca and Gavin Bryars – but really had few peers. Sigur Ros’s songs moved at glacial tempos, building layer upon layer of gauzy sound while crawling toward an inexorable crescendo. The material was energetic and arena-ready, but also spooky and pastoral: U2 via Middle Earth.

On Sunday, the band — now a trio augmented by a string section and a horn section, plus additional percussion and keyboard players — opened with the new song, “Yfirboro,” which unfurled slowly, morphing from a chorus of shimmering drones to a set of ascending chords that gradually increased in volume and intensity. In other words, Sigur Ros was getting back to its roots.

Since its second album, “(),” Sigur Ros has struggled to balance its pop and experimental impulses. The band’s last several records — “Takk,” “Med Sud I Eyrum Vid Spilum Endalaust,” and “Valtari” — have sidelined guitars in favor of ornate string and horn arrangements. Shrieking otherworldly tones gave way to the gentle plink-plonking of electronically treated music boxes and lush string arrangements. The music was never unpleasant, but it was benign and, at times, overly precious — the aural equivalent of lighting a scented candle. That material, like the piano-driven “Hoppipolla,” provided some of the evening’s snooziest moments.

Sigur Ros’s newer songs — which will be included on the band’s forthcoming record, “Kveikur” — struck a darker tone, particularly set-closer “Brennisteinn.” The song pitted Jonsi’s melancholy vocals against a menacing bass squelch and disjointed industrial-sounding percussion. Following an hour’s worth of mellow and harmonious fare, it came as something of a relief.

Whatever mood the band is shooting for — be it broody, woozy or twee — Sigur Ros songs tend to retain an epic, big-screen feel, which the band amplified on Sunday by broadcasting projections of oceans, ice, crystals and mountains against the stage. The light show might have been a waste, though. As the band accelerated into the endless crescendo that closes “Popplagio,” a glimpse around the room revealed that more than a few people in the audience preferred to listen with their eyes closed.

Leitko is a freelance writer.