Instrumental Greensboro duo The Bronzed Chorus has a secret weapon behind its intense though spare post-rock approach: Brennan O’Brien is able to drum with enough power and dynamics with just three of his limbs that he doesn’t need his fourth. Well, at least not for drumming: During live shows, O’Brien’s left hand mans a keyboard that sits just next to his hi-hat, supplying guitarist Adam Joyce with a sturdy bass counterpoint. Live, it’s interesting to watch, but can such utilitarianism translate well to a record?

Yes, it seems. On I’m the Springthe Triad twosome’s second studio discO’Brien and Joyce benefit from the freedom of playing just one part at a time, as well as significantly cleaner production than that of debut LP thurtythurty, a two-day project tracked in Joyce’s bedroom. Their compositions and attention to detail become a bit clearer, and they’re able to communicate beyond the build and the climax.

On opener “Underpass Sunrise,” the 30-minute disc’s standout, a squirrely guitar hook chimes incessantly, winding its way through a drum build and a thick keyboard throb. The lead line explodes through a fit of distortion, spilling out over pounded skins. As the final passage kicks into double time, Joyce’s strum spirals out of control. The duo shatters the track into shards and spent shells. Meanwhile, “Tiny Oxen” is a slow riser that gradually adds drama before teasing a huge climax. With its intoxicating shimmers, closer “E.D.W.D. On Georgia” appropriately delivers the band’s biggest finale.

These tension games are nothing new in indie rock, and The Bronzed Chorus isn’t stretching the vocabulary or palette of its instrumental peers. But the duo’s bare-bones approach still yields something substantial, suggesting that there are still crevices they can explore in this familiar form.

The Bronzed Chorus plays a free show Thursday, Oct. 15, at 10 p.m. at Tir Na Nog and at Duke Coffeehouse at 9 p.m. Saturday, Oct. 17. Tickets are $5.