Foo Fighters announced Tuesday a new album and a one-day festival as the alternative rock titans promised their heaviest sound yet.

Weeks after releasing a hard-hitting single, Foo Fighters said that their ninth studio album, "Concrete and Gold," would come out on September 15.

Dave Grohl's band, which had appeared to be lying low earlier this year, said it had quietly spent six months working on the album with Greg Kurstin, the producer best known for co-writing Adele's smash hit "Hello."

The group made clear it was not moving toward Adele's ballad style. The band called it "our biggest sounding album ever."

The album "will undoubtedly fry stereos from here to Fukuoka. Start saving your speaker money now. Sorry. It's big," said a handwritten note posted on its website.

"Concrete and Gold" has "more twists and turns than a live Senate hearing," it said.

Foo Fighters also announced that they would headline a one-day, rock-driven festival, Cal Jam 17, on October 7 in San Bernardino, California.

The lineup will also include Liam Gallagher of Oasis fame, desert rockers Queens of the Stone Age and garage rockers Cage the Elephant.

Foo Fighters, born from the ashes of Nirvana in 1994, have frequently hinted and dispelled speculation of retirement.

The band earlier this month released a first song from the album, "Run," a shift back to the intense, whirling guitars of Nirvana in which the 48-year-old Grohl was the drummer.

"Run" was accompanied by a video directed by Grohl in which residents of a retirement home erupt into a raucous party when Foo Fighters come as their evening entertainment.