Tool keeps it big and oppressive -- yet alluring

“Prog,” short for “progressive,” was a dirty word once, a smear for a genre of ‘70s arena rock known for its excess and self-importance. Punk was supposed to bring an end to that kind of self-indulgence, but when prog fully reemerged in the ‘90s, its most inspired sounds were equally rooted in the alternative nation, going very big and very dark in the hands of Tool and other young acts, minus tales of misty mountaintops and bass solos without end.

It’s become a setting for some of the most ambitious sounds of modern hard rock, stretching beyond Tool to encompass the intensity and scope of System of a Down and the Mars Volta. Tool bridges those generations. The L.A.-based band delivered two hours of brooding sounds and images on Thursday, the first of two nights at Staples Center.

The sound could be contemplative or raging but was always in complete control and a servant to Tool’s fully realized vision, most recently mapped out on the album “10,000 Days.” The music was sweeping in scope and remained precise, built on the most minimal of elements cranked up to a great, undulating sound.

It was big, oppressive and strangely alluring, carefully constructed around the guitar of Adam Jones.

Bassist Justin Chancellor plucked the crisp melodic pattern of “Jambi” as singer Maynard James Keenan wailed: “You’re my peace of mind, my home, my center / I’m just trying to hold on one more day.”

Keenan was a more approachable presence at Staples than he has been on earlier tours, waving warmly to fans at stage-right, though sometimes still singing in profile or even occasionally with his back to the crowd.

Visuals, a big part of the Tool arsenal, included images of dementia and decay, mushroom clouds and grappling bodies, brain cells and distant galaxies splashed across several video screens. It was something like those old prog shows of the ‘70s, with green laser beams slicing the air. Drummer Danny Carey even had a gong.

The overall effect was dark and often challenging, and somehow universal enough to find an audience big enough for two nights at Staples, where fans could count on finding something exciting and cathartic in the gloom.