Jazz Tap Ensemble.

I'm not sure what I was expecting. Maybe the glamorous big-screen Hollywood feel of a Fred Astaire extravaganza. Or the funky acrobatic splendor of the hoofers' segment of last fall's Riverdance, hyped to a Broadway hilt. As it turns out, that's not what the five-member Jazz Tap Ensemble is all about. Tapping to the tunes of a live jazz trio, this group espouses milder virtues, foregoing showy tricks for intricate studies of rhythm, balance, and sound.

On a proscenium stage, which gears its audience for spectacle, this kind of subtle kinetic inquiry can seem humdrum. And indeed the concert stage setting of the Joyce Theater served to diminish the efforts of the ensemble's dancers. Only the two men of the company came alive under the lights, their entire bodies responding to and counteracting their flying feet. The women, tapping valiantly and well, often looked shy in comparison, their upper-body carriage apologizing for the authoritative rat-tat-tat being issued below the knees. For aficionados of the form, a tapper's rhythmic accuracy and daring or a briliantly syncopated riff may measure talent. But the Joyce's more general audience, myself included, will long for real stage presence, the energy and charisma that separate the pedestrians from the performers.

Sam Weber, the ensemble's leading man, and the younger Channing Cook Homes could hardly be more stylistically distinct. Weber mixes Astairesque elegance with the fleet awkwardness of Ray Bolger's Scarecrow in The Wizard of Oz. Dancing, he skims the floor, propelled by a metallic torrent, only to bound suddenly into the air, buoyant, eluding the grasp of gravity. His demeanor remains, for the most part, utterly, inwardly intent, as if the were held in thrall by his own rhythms. But now and again his focus shifts, and he bestows an irresistible beatific smile on those of us relegated to the outer world, who can hear but not feel those magical taps.

Holmes takes a down-to-earth approach. Bending forward, he stamps and smashes out of a powerful tattoo, a direct and vibrant address to the ground beneath his feet. Reveling in the fun of it, he lets his hips rock and his arms fly, moving with juicy abandon. And he, like Weber, is transported by the unrelenting patter of the dance.

Even with these two inspired performers, the Jazz Tap Ensembles can't quite hold together an evening-length program. The choreographic material -- a medley of bits and pieces -- contains numerous brief passages of impressive hoofing but very little spatial craft or dramatic structure, giving the concert the feel of a variety revue. And videographer Dennis Diamond's attempt to spiff things up with live projections of furiously tapping toes was only window dressing. The ensemble's artistic director, Lynn Dally, clearly has a monumental task ahead: finding out what turns tap into theater.