Last Thursday, the Iron Horse Music Hall was crowded, and nobody noticed as three men shuffled their way to the front of the room and ascended the stairs to the stage. The upright bass lay on its side, and a grand piano stood poised on the stage, its lid opened halfway with microphone cables streaming out in several directions from inside. The drums sat on the opposite side of the stage, the four tiny drum shells lying in the shadow of three ride cymbals.

• Slideshow: The Bad Plus at The Iron Horse

There were no announcements, no applause, just the clatter of silverware on plates, the low, buzzing murmur of patrons talking over appetizers and waitresses taking orders. The lights dimmed as The Bad Plus arrived at its instruments. The audience quieted, turned their heads to the stage, and the show began.

Two clicks from the drumsticks, and the band launched into its first tune, a new piece by bassist Reid Anderson, “about a shy girl in high-school,” entitled, “Beryl Loves to Dance.” There was a burst of a fluttering, major melody, establishing the themes of the tune.

Anderson was hunched over his instrument from the beginning, striking octaves on the upper register, while Dave King, the drummer, was stooped over his set, laying down furious sixteenth notes on the hi-hats, grinning and laughing to himself as he played. Ethan Iverson was perched over his piano playing the melody, each hand shaped into a claw, banging wildly, yet remarkably controlled, on the keyboard.

The melody built to a triumphant anthem of major cadences. There were several breaks scattered throughout the tune, catching the audience off guard each time, bringing the music down with a swing or funky beat, sometimes accompanied by an atonal piano solo. Every time King reached a percussion climax, he would hit a cymbal and stand up briefly, as if the inertia of the drumstick in his hand had carried him out of his seat. The song ended with a crescendo of cymbals followed by King scraping the metal wires underneath his snare for a quiet, scratchy, tinny sound.

The Bad Plus played another new, jazz-fusion and progressive-rock influenced song before breaking out its classic “And Here We Test Our Powers Of Observation” off their album, Give, which featured heavily composed and tightly arranged melodies, bombastic drumming and dynamic changes in volume, meter and key.

At this point, Iverson stood up to accept a hearty applause, and introduced the band, while King and Anderson improvised a goofy drum-bass duet to accompany Iverson’s words. He sat back down to begin a song he recently wrote called “2 PM,” which was strictly composed but still had a free, loose sound. Anderson went for a bass solo, accompanied by King hitting surprisingly straight and simple quarter notes on his ride cymbal. Anderson faded out, leaving King to play a solo on his floor tom with his left hand, while pressing the stick in his right hand against the head of the drum to tune and change the pitch of the drum.

New songs and classic compositions from previous albums were performed, and the audience was exposed to sometimes abrasive and irregular time signatures, key changes, syncopation and several moments of The Bad Plus’ patented, boisterous explosions of musical climax.

A new Anderson piece, entitled “Snowball” was introduced, and its serenity washed over the audience, cleansing the musical pallet, starting afresh, from almost silence. Its tranquil, pastoral melody calmed the listeners and sounded similar to the calm before another raging storm of thundering polyrhythm and modulation. It ended so gradually that the audience didn’t clap until at least fifteen seconds after the music ended.

After the classics “1979 Semi-Finalist,” and “The Empire Strikes Backwards,” they played an Anderson piece called “Dirty Blonde.” The grand theme was announced by piano until it resolved to a breakdown. Next came a piano-heavy bridge.

There was no clear distinction between soloist and accompanists, as all the members improvised simultaneously. The interplay was incredible as themes and figures were passed between each player, creating a cohesive sound. The collective jam continued, invoking emotion in the crowd in the form of bobbing heads and intense gazes.

Their final song of the set was “Lost of Love,” another Anderson composition. It featured a melancholy but hopeful melody, which reached its peak before collapsing gracefully into sustained, minor solo piano chords. The melody was retold, each time more triumphant, more reassuring and more hopeful, until everything stopped, and a few carefully selected piano keys were tapped to end the set.

The band walked off stage, and Iverson accidentally kicked Anderson’s upright bass as he walks past it. As they stood talking and joking, the audience cheered and applauded while watching their conversation in a curious voyeur moment.

The Bad Plus returned to the stage and played “Flim,” by Aphex Twin. Then the group began the jazz standard, “Have You Met Ms. Jones?” This stylistic change started like a typical rendition of the tune, until they smoothly sped up the tempo mid-chorus. The song culminated in a stunning finish where the band teased the final part of “Physical Cities” from their album Prog.

The ending was an incredibly syncopated series of hard hits with varying lengths of rest in between. For fans familiar with this composition, this ending was a big tease, leaving them wanting the complete song while also finishing the concert with an invigorating and heady piece of music.

In an interview after the show, Iverson said that while on tour, The Bad Plus rarely has devoted practice time, and uses sound checks to work out new songs and variations to the repertoire. When Iverson composes, he explained, he simply sits down at any piano and, “sometimes it comes,” but most times it doesn’t.

King spoke about playing complicated music, saying that, for time signatures that are not standard 4/4, practicing the piece is the only way to become comfortable with it. For King, playing in odd time signatures is just another way to approach music. King also shared that several years ago the band tried to learn Anderson’s complex composition “Physical Cities” by reading the music a few times until the group tried to perform it one night in Pittsburgh, and it did not go well. The piece was then put aside until everyone had memorized it. Now, King says he knows the piece so well that rather than counting the meter to place the hits in the correct places, he just feels it happen.

All three band mates use unorthodox, powerful and wholly original approaches to composing and performing music. Each player is just different enough from one another  to combine into the sleek collective that is The Bad Plus. They took the Iron Horse by surprise Thursday night, capturing minds and ears from the first click of the count-off to the first song, to the last sustained wail from the piano.

Ben Silverman can be reached at [email protected]. Craig Holland can be reached at [email protected].