Shannon Gunn, right, with Hope Udobi, center, on keyboards, and Kelton Norris, left, on drums, at Columbia Station. (Astrid Riecken/For The Washington Post)

Four people sat in the house at Columbia Station when trombonist Shannon Gunn and her Firebird Organ Trio got started on a Tuesday evening in November. By the end of the first set, the audience had grown to 12. Gunn not only took the sparse attendance at the Adams Morgan restaurant and bar in stride, she also treated it just as she would a sellout crowd.

“Any requests? Anyone want to sit in?” she asked after she, keyboardist Hope Udobi and drummer Tyler Leak had finished the first tune. “Anybody here from out of town tonight?” A man at the far end of the bar said he was in from Seattle. “Well, you’ve found the right place for jazz on Tuesday nights,” Gunn said, then immediately corrected herself: “There’s actually a few good places, and this is one of them.”

Indeed, if Gunn and her adventurous music had a sparse crowd, they also had hefty competition. Tuesday night in the District sees no less than three long-term jazz residencies — saxophonist Tedd Baker at JoJo, Gunn at Columbia Station and saxophonist Elijah Easton at Service Bar — located a few blocks apart. All have free admission, and they’re staggered in their time slots. An intrepid jazz fan could drop in on all three.

Tedd Baker, left, on saxophone with Quincy Phillips, center, on drums and Kris Funn on double bass at Jojo Restaurant and Bar. (Astrid Riecken/For The Washington Post)

Baker’s weekly stand at U Street’s JoJo Restaurant and Bar begins at 7:30 p.m. His trio’s personnel can vary, but the core unit comprises bassist Kris Funn and drummer Quincy Phillips. Sit-ins aren’t unusual; Baker, 44, encourages players of all abilities to bring in their axes.

Also a common sight: a packed crowd in the small brick basement room, where Baker draws listeners of all ages, races and backgrounds, including tourists and curious passersby who glimpse the bandstand and its eerie lighting, alternating green and purple, through JoJo’s bay window.

Regardless of who’s in the crowd or on the stage, the focal point remains Baker’s tenor sax sound: sinewy and lyrical, attacking whatever tune comes up — whether Duke Ellington or Michael Jackson — with cascades of melody and swing that are fast-paced but never cluttered. When they’re behind him, Funn and Phillips are as tight and sympathetic as a rhythm section gets.

The rules, Baker says, are few but ironclad: “Completely trust in the cats playing, yet hold each other accountable. [Do] not be afraid to fall on our faces. Pull from the tradition forward and ultimately play our style, our personal concepts, and beyond.”

Gunn’s Firebird Organ Trio takes the stage in Adams Morgan at 8 p.m. Like Baker, her personnel changes frequently — weekly, in fact. It’s not even always an organ trio, although Gunn (who prefers not to state her age) uses the quirky trombone-organ-drums instrumentation as often as possible.

The crowd size at Columbia Station also varies each week. The restaurant’s capacity is only 40, including the bar (though the space is long and wide, with bare wooden floors that carry the music throughout), so even a full house isn’t a packed one. There are devotees, though, that form a regular presence.

“You see a lot of the same people,” Gunn said. “It’s like family. It’s just a really comfortable place to hang out.”

As for the music, it’s as bold and risk-taking as its unconventional instrumentation suggests. Mehari Woldemariam, who owns and books Columbia Station, gives Gunn free rein to “get creative” — including lots of original tunes and even some completely improvised pieces. At the November performance, Firebird took an audience request for Mongo Santamaria’s “Afro Blue” but subverted expectations, rendering it as high-octane funk that was unlike any recording of the jazz classic.

Saxophonist Elijah Easton performs at Service Bar, whose jazz gigs start at 10 p.m. Tuesdays. (Astrid Riecken/For The Washington Post)

Easton’s stand at U Street’s Service Bar, which begins at 10 p.m. (despite what it says on the bar’s website, which carries a 9 p.m. billing), is probably the loosest, most free-flowing of the Tuesday night residencies. It makes sense, since Service Bar is also the coziest and most casual of the three spaces, with two-top tables lining one wall and metal stools filling out the rest. Service Bar, which has a small food menu, is Tuesday’s most drinking-intensive jazz spot. Easton, 27, knows that a strict routine won’t fit there.

“It’s a dynamic gig,” he says. “That’s part of what makes it hip.”

The Tuesday before Thanksgiving, for example, the place was crowded — with everyone but Tarus Mateen, Easton’s regular bassist.

Mateen also wasn’t answering his phone. “Who else can we try?” Easton asked drummer Dana Hawkins as he assembled his tenor saxophone. They called a few other local favorites, none of whom answered, before simply shrugging and deciding to go on as a duo. They began a hair-raising performance of Thelonious Monk’s “Evidence,” dueling as much as they synchronized, with responses and one-ups throughout.

Halfway through, Steve Arnold, a 23-year-old bassist who has already earned significant respect on the D.C. scene, sidled in behind them, seemingly out of thin air, quickly unpacking and plugging in an electric bass. They finished “Evidence” and started into the bebop blues “Now’s the Time” with Arnold giving it a slippery funk feel that was more James Brown than Charlie Parker. The tune almost immediately burst out of its blues form and into a long, unbridled jam, Easton charging forward like a cannonball as Hawkins was pulling one of the bar stools toward him. He played it like a snare drum. Chatty, 20-something jaws dropped.

Even at these recurring bar gigs, one quickly learns to expect the unexpected.

If you go

Tedd Baker: Tuesdays at 7:30 p.m. at JoJo Restaurant and Bar, 1518 U St. NW. Free.

Firebird Organ Trio: Tuesdays at 8 p.m. at Columbia Station, 2325 18th St. NW. Free.

Elijah Easton: Tuesdays at 10 p.m. at Service Bar, 928 U St. NW. Free.