The trio keeps it simple in the studio

"We multitask," Mr. Arnold explained. "It's kind of fun, too." At times, concertgoers don't believe what they've seen and think the band is using prerecorded music as part of the act.

The trio keeps it simple in the studio, as evidenced by its two albums—last year's self-titled disc, and 2009's "Only Way to Be Alone"—both on the Sargent House label. "We won't record anything that we can't play live," Mr. Schwartz said.

Topped by flawless vocal harmonies, the trio's breezy, spirited music is a throwback to the best folk rock of the late 1960s and early '70s. One can hear in their sound a bit of Simon & Garfunkel and Crosby, Stills and Nash—especially the songs featuring Graham Nash, who recently called the band to express his admiration. Good Old War seems a natural for Deadheads and jam-band fans who favor the Grateful Dead's "American Beauty" period. It's no surprise to learn the trio cut its teeth by performing songs by the Beatles, the Everly Brothers, Paul Simon, the Traveling Wilburys and other pop acts that featured vocal harmonies.

"We were making acoustic pop songs," Mr. Goodwin said, remembering their days playing Philadelphia-area bars. "When we decided to do our own music, we said: 'Let's make good songs that can stand alone with just acoustic guitars and vocals.'" The voices seem to blend naturally. "At this point, it's memory," he added. "Even if we can't hear ourselves on stage, we can still sound good."