Anyone jarred by Alabama Shakes’ jump from the classic soul-rock of the band’s 2012 debut Boys & Girls—stirred by Brittany Howard’s volcanic vocals—to the mysterious, minimalist art-funk on follow-up Sound & Color should consider the alternatives.

“We’re all pretty much into heavy metal,” drummer Steve Johnson says. “Brittany likes Lamb of God, and I’ve always been a Pantera fan.” As for bassist Zac Cockrell, Johnson says, “He’s into anything where you can’t understand the lyrics, and he’s also really into pop-country. That boy loves some pop-country.”

Add influences from Ennio Morricone’s spaghetti-western soundtracks and R&B poet Gil Scott-Heron to Johnson’s discovery of experimental German rockers Can as well as the Fleetwood Mac instrumentals that Sound & Color co-producer Blake Mills threw into their listening stew. It’s no wonder that the Shakes broke bounds.

“There was a lot of experimenting,” Johnson says of Nashville sessions for Sound & Color, which was released in April. “We all wanted it to be better than our first album, and we knew that it was going to be different because our tastes and style had changed.… Everyone was interested in what the possibilities were.”

The group, rounded out by guitarist Heath Fogg and touring keyboardists Ben Tanner and Paul Horton, injected new wrinkles from fuzz-bass bombs to strings. “We’d stack cymbals on top of cymbals,” Johnson says, “turn them upside down, have cymbals on snare drums.” Howard laced songs with vibraphone and pushed her voice in unusual directions, unleashing pinched cries in “Don’t Wanna Fight” and playing otherworldly siren in the spacey “Gemini,” an opportunity to let loose in the studio’s echo chambers. “We took full advantage of those,” Johnson says. “There were times where she would go in and, in one take, ‘Boom!’ ”

Alabama Shakes have changed onstage as well. As the group heads for a Sept. 27 Boston Calling finale, sets have proven more moody and sophisticated, distanced from the band’s original style, especially with the omission of breakthrough hit “Hold On.”

“We got a little burned out on playing it,” Johnson says from a California tour stop. “If you’re going through the motions and there’s no feel there, it doesn’t really make sense to do it.”

The Shakes have been through the motions, from the daily grind of odd jobs to playing tiny bars. Before landing a post office job, Howard worked as a parking lot attendant. “I’d see her just chillin,’ smoking cigarettes and not doing anything,” says Johnson, a FedEx deliveryman at the time. “We’d talk about what songs we wanted to jam on.” He went on to a better job at a nuclear plant, but explains, “You’d have to dress up in one of those suits like you see in Back to the Future.”

They’d met as teenagers in Athens, Ala., Johnson says. “We played shows together, like small garage-punk shows or whatever. We were just young, dumb kids hanging out at parties.”

But Howard blossomed as a singer—and found a musical accomplice in classmate Cockrell. The three launched the Shakes, recruited Fogg and moved from playing James Brown and Led Zeppelin covers in nearby Huntsville to hitting Birmingham and Nashville, bigger cities that accepted original music.

“It was worth it to drive there,” Johnson says, though he adds, “We’d probably drink whatever money we made.” They finally got a song posted on the influential blog Aquarium Drunkard, prompting the Drive-By Truckers’ Patterson Hood to catch a show and inform his managers—among other suddenly interested parties. “It kind of snowballed,” Johnson says. “We got a good team.”

Critical acclaim and Grammy nominations followed. Given her powerful presence, Howard garnered the most attention and drew predictions that she’ll eventually fly solo (in turn, Howard just released an album by side project Thunderbitch, revisiting her garage-punk roots). But that talk doesn’t bother Johnson.

“If that’s the direction that she goes, I say more power to her, because I know she can do it,” he says. “There’s always gonna be our thing, but she’s going to do her own thing, and that’s cool.”

Alabama Shakes play Boston Calling at City Hall Plaza on Sept. 27.