Dirty Projectors frontman Dave Longstreth has never been afraid to get heady. Back in 2004, when he was the sole constant member of the group, he released “The Getty Address,” an electronically arranged operetta that mashed up topics as varied as Hernan Cortes and Eagles songwriter Don Henley. The band’s 2007 breakout, “Rise Above,” was an avant-pop reinterpretation of “Damaged,” an album by the hardcore punk band Black Flag. Unless you accompanied your listening with some deep reading on the band’s Wikipedia page, it was hard to catch all of the references.

But lately, the sextet — which has since congealed into a semi-stable lineup, revolving around Longstreth and vocalist/guitarist Amber Coffman — has lightened up the conceptual load a little.

On Friday night at the 9:30 Club, the group performed the first of two sold-out shows, a 74-minute set of material drawn from its newest record, “Swing Lo Magellan.” On this batch of songs, they’ve dialed back the knotty time signatures and tamped down the weirdness by tossing in a few swatches of mid-’70s folk rock.

Even in its most accessible moments, Dirty Projectors’ music relies on a confounding mix of sounds. Longstreth’s elastic lead vocals are frequently accompanied by frenetic harmonies sung by his female band mates. These backing melodies are sharp and sometimes dissonant, drawing inspiration from the vaguely alien sounds of medieval music rather than the Beach Boys. Meanwhile, guitar riffs get swiped from West Africa and the rhythm section plays a wobbly take on contemporary R&B grooves. It’s intellectually stimulating stuff, but not always sufficiently energetic to carry the band in a rock concert setting.

So a few old-school rock tropes go a long way. Midway through “Offspring Are Blank,” Longstreth kicked on the distortion pedal and plunged the band into a Neil Young-worthy rave-up. On “The Gun Has No Trigger,” the band took cues from vintage soul tunes, with the backing vocalists carefully ramping up their intensity in order to deliver a cathartic chorus. It’s these moments, when they effortlessly blend esoteric ideas with pop craftsmanship, that Dirty Projectors’ music is most rewarding.

Dirty Projectors remain cerebral, but throw in a welcome bit of pop craftsmanship. (Jason Frank Rothenberg/The Windish Agency)

But when that fails, they also have a certain amount of technical shock and awe on their side. Midway through the set the band performed “Beautiful Mother,” a composition drawn from “Mount Wittenberg Orca,” the group’s collaboration with Icelandic singer Bjork. Here, Coffman and the band’s other female members hopscotched through a series of polyrhythmic vocal lines that would have made modern composers like Meredith Monk jealous.