THE FIRST COUPLE OF THE BANJO: Abigail Washburn and Béla Fleck played material from their Grammy-winning 2014 album at Princeton’s Richardson Auditorium. (Photo by Jim McGuire)

Finishing their second or third piece of the evening, Abigail Washburn and Béla Fleck rose from their seats to acknowledge an appreciative full house in Princeton University’s Richardson Auditorium on Thursday. “Clapping sounds really good in here!” Ms. Washburn exclaimed, eliciting laughter and a further wave of applause. But if, superficially, her remark sounded like preening, it was also true. Every sound reverberated warmly in the intimate, wood-lined hall. Clapping did indeed sound good there. But more to the point, the space wonderfully supported each note of the banjo duo’s engrossing performance that evening.

Prompted by the birth of their son Juno, Ms. Washburn and Mr. Fleck began their official musical collaboration in 2013 in part as a way to keep the family together on tour. Their act is a coming together of two of the banjo’s foremost ambassadors. In a career spanning nearly four decades, Mr. Fleck has pushed the instrument well beyond its traditional role in bluegrass string bands (though he does that too). Perhaps best known for his pioneering work with the jazz-bluegrass fusion group the Flecktones, Mr. Fleck has also played extensively with jazz pianist Chick Corea, collaborated with bassist Edgar Meyer and tabla player Zakir Hussain, and composed and performed two concertos for banjo and orchestra. Considered by many to be his instrument’s finest technician, Mr. Fleck has been nominated for 30 Grammys — in more categories than any other instrumentalist in the award’s history — and has won 15 of those awards.

If the range of genres Mr. Fleck commands is sprawling, Ms. Washburn demonstrates by contrast that it is not comprehensive. From her 2005 debut solo album Song of the Traveling Daughter, she has staked out a corner of the bluegrass world uniquely her own, largely drawing on old-time Appalachian folk music traditions, but occasionally integrating elements of Chinese folk music. Ms. Washburn is fluent in Mandarin and her inclusion of the language in her singing is as impressive as it is unusual. She plays with a number of groups that range from old-time music (Uncle Earl) to bilingual, multi-genre experimentalism (The Wu Force).

In Princeton, Ms. Washburn and Mr. Fleck sat onstage ensconced in a little nest of microphones, cables, and six or seven banjos of varying size and pitch. The texture of the duo’s sound varied with each piece, but at no point did they sound thin or deficient. This was due in part to the many different instruments the two utilized. On “Little Birdie,” Mr. Fleck picked up a large cello banjo — strung an octave lower than his normal instrument — and instantly became their rhythm section, his rubbery bass lines grounding Ms. Washburn’s limpid vocals and fingerpicking, occasionally thumping the head of his instrument in emulation of a kick drum. In the next piece he reversed course, teasing out intricate trebly lead lines on a diminutive mandolin-sized instrument.

But even when they were both playing standard five-string banjos, each complemented the other in timbre and style. Mr. Fleck played with a rolling three-finger style developed by Earl Scruggs, full of ringing open strings droning along with his melodic playing. He wore metal picks on the fingers of his right hand, giving his notes a keen brightness. Ms. Washburn eschewed picks for the more muted, clucking sound of old-time clawhammer technique, striking the strings of her instrument directly with her fingers. Playing together, the two simmered, with Ms. Washburn’s penetrating, full-throated vocals soaring above their picking.

One of the evening’s highlights was “Shotgun Blues,” a searing “old time murder ballad” Ms. Washburn wrote, in which a lady — and, as she explained, it’s inevitably the ladies who are the victims in this narrow genre — plots her revenge on a no-good man. The song stretched between a spare, rattling introduction, with both musicians beating ominously on their instruments, and a howling coda with both playing at full tilt — a musical tension that mirrored the speaker’s vacillation between restraint and murderous fury.

Most of the material Ms. Washburn and Mr. Fleck played was from their self-titled 2014 album, though the duo also opted to test-run a few new songs. But whether the songs were familiar or not, the audience hung on their every note. After their performance, when the duo came back onstage for an encore, Ms. Washburn proposed they play one of three songs. Audience members clamored indistinctly for their favored number for a few moments until Ms. Washburn, grinning, asked, “Well, do you have enough time for all of them?” We did.