Boston-based roots trio Ballroom Thieves bring authentic folk/rock to Nightfall

Special guests are kind of like jam filling inside an otherwise run-of-the-mill doughnut. They're a special surprise that adds a little extra dimension to the music you already love.

Usually, a band's lineup might be bolstered by the addition of one, maybe two, special guests. Earlier this year, however, Boston-based folk rock trio The Ballroom Thieves played a string of dates featuring quite a few more than that.

"We took the Maine Youth Rock Orchestra on the road," says guitarist Martin Earley, who co-founded the band in 2010 with percussionist Devin Mauch.

The orchestra, which is based out of Portland, Maine, features dozens of musicians ages 7-18 who perform symphonic renditions of selections from the rock and classical music repertoires. In all, 26 musicians accompanied The Ballroom Thieves for eight dates last month.

"It's really nice to play your songs with a whole orchestra backing you up," Earley adds. "When you're used to that for a few days, you go back to the trio, and it sounds a little empty, but we've been doing this for so long as a trio that we're used to it."

On Friday, May 20, The Ballroom Thieves will tour, just the three of them this time, to Chattanooga, where they will make their Scenic City debut as the headliners of the Nightfall Summer Concert Series.

Although they met while both were enrolled at a small college outside Boston, Mauch and Earley brought wildly different musical backgrounds into the mix. Mauch was formerly a singer in hardcore and alt-rock bands. Earley found his way into the musical fold through the classic rock and country artists his father listened to.

The band's secret weapon, however, is Calin Peters, a classically trained cellist who studied at Boston's Berklee College of Music and whose melodic versatility gives the band more sonic oomph and creative freedom.

"One thing [the cello] does definitely is open up a lot of space," Earley says. "With three people, we can do what some bands do with five people.

"She can cover a fourth harmony or third harmony and make our sound much thicker and deeper than it otherwise would be. For three people, we make quite a bit of noise, and that's something the cello is heavily involved in."

In 2015, The Ballroom Thieves released their debut LP, "A Wolf in the Doorway," a 12-track record featuring pining vocal harmonies, unadorned acoustic instrumentation and intensely personal songs that drew comparisons to bands such as The Head and the Heart, Green River Ordinance and Rascal Flatts.

The band is in the final stages of work on a second album and, if anything, it reflects musicians who have matured in their craft, are more seasoned in their songwriting and more comfortable than ever with themselves. Even though the band's lineup is back down to just three people, Earley says those qualities should all shine through and grab the audience on Friday night.

"One thing all three of us feel pretty strongly about is that when people come to our shows, what they see is what they get," he says. "We feel like the authentic side of the music is what calls to us the most, and that comes through when we play.

"We're all up there playing pretty personal songs, so the best thing for us would be for the audience to hear a song and know that it's about something that they don't know about but for them to still identify with it personally. We want to connect with the audience, and that feeds the energy both ways."

Contact Casey Phillips at cphillips@timesfreepress.com or 423-757-6205. Follow him on Twitter at @PhillipsCTFP.