To anyone who hears it in passing, the name Zac Brown Band might mean country music, beards, or the man himself: Zac Brown, who formed the group in 2004. But the eight-member band, whose recently released fourth album, "Jekyll + Hyde," ranges from Gaelic roots to hard-rock undertones, is quickly proving much more than just one man or genre.
The lineup — with Jimmy De Martini, John Driskell Hopkins, Coy Bowles, Chris Fryar, Clay Cook, Matt Mangano, and Daniel de los Reyes — are musicians from a wide variety of backgrounds. Reached by phone in separate interviews prior to their setting out on a tour that comes to Fenway Park on Friday, De Martini, Bowles, and Cook described how the leader's increasing openness to collaboration had provided opportunities for them all to pitch in with the songwriting.
What resulted is an album Cook describes as "musically schizophrenic," befitting its title. "It's not necessarily country music; it's just that country radio plays us, and they've given us a home," he says. "It's always been 90 percent what we feel like the song is asking for, and the other 10 percent is our own fancy, seeing what we can come up with," Bowles says.
De Martini, the band's fiddler and a harmony vocalist, was the first permanent member to join the Zac Brown Band in 2004. Coming from a mixed background of classical violin and rock guitar, he merged what he describes as his "two different worlds" when he signed on.
"Zac has always collaborated," he says. "But he used to work with just one person, and now he's open to four or five people having ideas on one song."
On the first three Zac Brown Band albums — "The Foundation" (2008), "You Get What You Give" (2010), and "Uncaged" (2012) — Brown worked closely with songwriter Wyatt Durrette to create tracks. But on "Jekyll + Hyde," he enlisted Niko Moon as a songwriting partner — and reached out to his bandmates as well.
"It's awesome that everyone can have input," says De Martini. "It's a recent thing for me. [Zac's] encouraged me to contribute more recently, because I always have been a little timid to show people the stuff I write. He encourages everybody to be a part of the writing process, so it's definitely more of a team effort these days."
Bowles, enlisted in 2007 to play guitar and keyboards, has watched this open approach materialize. "It's a pretty cool democracy, in that when one person's writing, they come to the table and say, 'Look, here's this huge song, but I don't have a bridge to it,' " he explains. "Everyone's accustomed to throwing stuff out there and seeing what sticks."
And as the band has grown, so too has Brown's eagerness to collaborate more widely. Tracks like "Mango Tree," a jazzy duet with Sara Bareilles, and "Heavy Is the Head," a rhythmic rock venture featuring Soundgarden vocalist Chris Cornell, are just a few examples on the new album.
With the studio transformed into a hive of ricocheting ideas, Bowles describes songwriting as "a really magical process. You don't realize how beautiful an idea is until you do it with other people. There's this really shimmery, awesome thing when you start finishing a song — where the song just starts writing itself." A riff might unfold into a four-tiered vocal harmony, a rich blend of tenors that cascades toward Brown's voice; working spontaneously infuses the band's songs with a distinct flavor: home-grown, and occasionally chicken-fried.
Cook — a blues-steeped player who attended Berklee College, and who in 2008 became the band's self-described "in the rafters" high harmonist, steel and acoustic guitarist, mandolinist, and keyboardist, after collaborating with John Mayer as Lo-Fi Masters and performing in the Marshall Tucker Band and Y-O-U — insists that the group doesn't write primarily for recordings.
"With 'Jekyll + Hyde,' we were really starting to think of how this would play in a show," he explains. "We're not really an album band. The album is basically a business card to get people to see us play live."
And whatever the disparate parts that go into the music, De Martini says, "at the core, everything still sounds like the Zac Brown Band. It has our signature sound of harmonies, guitar and melodies. And our songwriting has the storytelling — it comes from us writing about real things that people go through in real life."
There's no master plan setting the band's agenda, he adds. "It's an organic process. It's our music, and as long as our fans seem to enjoy it, are into it, and we're having fun, then that's all we care about."
Zac Brown Band
At: Fenway Park, Friday-Sunday at 6:30 p.m. (Saturday sold out)
Tickets: $61.50-$101.50. www.livenation.com
Mallory Abreu can be reached at email@example.com.