It could have been a big problem. Sex Mob's drummer, Kenny Wollesen, couldn't make it to Johnny Brenda's on Tuesday night, so the New York "downtown" avant-jazz band did what it was put on earth to do: Improvise.

Luckily, this was a triple bill presented by the Ars Nova Workshop. The preceding set was a drum duo featuring Billy Martin, of groove-jazz trio Medeski Martin & Wood, and Philly's Calvin Weston, a former Ornette Coleman sideman. It was an alt-jazz convergence: Both drummers, like Sex Mob slide trumpeter Steven Bernstein, were once members of the Lounge Lizards.

Weston gladly stayed on for the Sex Mob set. Bernstein, a kinetic front man in normal circumstances, was aflame here: He cued Weston all the way and steered the band, including alto saxophonist Briggan Krauss and bassist Tony Scherr, through an hour-plus meta-arrangement, blending disparate ideas.

Andrew D'Angelo, on alto sax and bass clarinet, started off the evening in a compelling free jazz trio with bassist Evan Lipson and drummer Mike Pride. Martin and Weston followed with a perpetual-motion set involving tuned gongs, cowbells, talking drum, berimbau, pandeiro, and even some trumpet.

Playing Philly for the first time in five years, Sex Mob began with music from their 2006 release

Sexotica

. They were soon in the midst of an epic medley, beginning with Prince's "Darling Nikki" and "Sign 'O' the Times," then morphing into the Count Basie staple "Blue and Sentimental" - all held together with the glue of decadent, free-form funk.

Now Martin was playing drums again beside Weston. Saxophonist Elliott Levin and guitarist Tom Spiker had joined as well, swelling the Mob to seven. There was another unlikely segue, from the Who's "I Can See for Miles" to Buffalo Springfield's "For What It's Worth," refracted through the prisms of roadhouse shuffle blues and greasy soul-jazz.

Bernstein roared into a distorted vintage microphone. Krauss soloed with a sock in the bell of his horn. And Weston shrieked aloud, scrambling to keep the pace, intoxicated by the anarchy of it all.