Eighteen musicians were sardined onto the stage at the Slope Lounge in Brooklyn on a recent Monday night, passing around a ricocheting, Argentine rhythm and a series of harmonic flurries that seemed to open wider as the piece, “Tangoing With Delusion,” went on. As individual players stood up to solo, they played as if climbing a mountain in the midst of a rockslide: making their way boldly, rerouting constantly.

Erica Seguine, the tune’s composer, was facing the band, conducting with large, emphatic gestures and an ear-to-ear grin. Her group, the Erica Seguine & Shannon Baker Jazz Orchestra, has become something of a regular presence on this stage in Park Slope, where the saxophonist Joshua Schneider books a different jazz orchestra every Monday night.

There are plenty to choose from these days. Quietly, beneath the radar of even most jazz lovers, the big band has been charging back. For a long time, the large ensemble has seemed a clunky vestige of American music’s past — outmoded since bebop supplanted swing in the 1950s — but a bumper crop of enterprising, conservatory-trained composers sees it differently: as a vessel of grandiose possibility.