Slightly reinvented, they're still rock's diffuse explorers

Sonic Youth isn't quite self-conscious enough for the title of its 16th album,

The Eternal

, to refer to the band itself. But it's hard to imagine a time when Sonic Youth didn't exist.

Over the course of almost 30 years - longer, from the looks of it, than much of the audience at Thursday's show at the Electric Factory has been alive - the art-rock band has insinuated itself into the fabric of American culture to the extent that it now seems inseparable from it.

Onstage, the band's core quartet - Thurston Moore, Kim Gordon, Lee Ranaldo and Steve Shelley - looks much the same as they did a decade and a half ago: the gangly, towering Moore flailing bonelessly at his guitar, Gordon stoic in a shimmering minidress. Even the ratio of salt-to-pepper in Ranaldo's hair has shifted only slightly.

The most significant change in the band's profile is the addition of former Pavement bassist Mark Ibold, replacing departed multi-instrumentalist Jim O'Rourke. A more solid and conventional player than the avant-garde O'Rourke, Ibold locked in with Shelley's drumming to give the band the most robust and propulsive rhythm section in its long history. Gordon, never a traditional timekeeper, still picked up a four-string on occasion, but she spent most of the set playing sporadic guitar, accenting riffs, or adding squalls of noise to the already exhilarating din.

Ibold's arrival has freed Sonic Youth to reinvent itself, turning toward traditional song structures while holding onto the more diffuse explorations of their latter years. In other words, they rock.

The songs from The Eternal, which the band played almost in its entirety over the 100-minute set, managed to hold together even as they flew apart. In "Anti-Orgasm," a swirl of chugging guitars parted abruptly to make way for a crystalline riff, while the unison thump of "Antenna" competed with a fluctuating whine that Ranaldo controlled with an effects box clamped to his microphone stand.

When the band did look backward, it looked way back, drawing from its late-'80s classics Sister and Daydream Nation and closing out the set with "Death Valley '69," a song first released a quarter-century ago. The song's monster-movie take on the Manson murders now seems a little snot-nosed, but its underlying dread has only deepened over the years. Detached from time and place, it seems ageless. Eternal, even.