By the mid-1990s, Dutch pianist Misha Mengelberg’s Instant Composers Pool Orchestra was one of the glories of European improvised music. Over the course of nearly two decades, it had slowly evolved into an elegant self-regulating mechanism, a gyroscope balancing composed material with ad hoc content, jazz with chamber-music accents, and its pocket-size sections (two brass, two reeds, and two strings–namely cellist Ernst Reijseger and bassist Ernst Glerum) with each other. But Mengelberg likes chaos, so in 1996 he threw a wrench in, enlisting second cellist Tristan Honsinger, who’d already put in a stint with ICP in the 70s. A natural anarchist with long experience in improvised theater–which has made him an ally to ICP’s drummer-showman, Han Bennink–he gave the band a booster shot of instability. (I’ve seen him walk onstage during a quiet duet, pushing a broom and singing like an idiot.) When Honsinger first rejoined, his lurching entrances, mangled melody statements, and mistimed riffs made the gyro wobble a bit too much, but gradually the band righted itself. After Reijseger left in 1998, ICP drafted violist and violinist Mary Oliver, who’d played with Honsinger elsewhere and could bridge the distance between his eccentric timing and Glerum’s swinging pulse. Nowadays the string trio feels like a section again, albeit spikier than before, less polite, and more assertive in the upper register. (Oliver’s solo CD Witchfiddle foregrounds what this interpreter turned improviser brings to the mix: a sleek sound and conceptual clarity.) Honsinger takes center stage on ICP’s spanking new and very fine Oh, My Dog! (ICP), contributing an informal suite of five compositions–versus one by resident composer Mengelberg, one by clarinetist and saxophonist Michael Moore, and a cut-up version of Charles Ives’s already subversive “Country Band March” by reedist Ab Baars. The cellist has a knack for writing pieces improvisers can run with: catchy, harmonically simple ditties sometimes buoyed by Italian folk-dance rhythms. (He spends a lot of time in Italy, and on the title track croaks in Italian and English.) On the disc’s five collectively improvised pieces, however, Mengelberg’s influence is still paramount–not least because trumpeter Thomas Heberer and trombonist-of-a-thousand-faces Wolter Wierbos employ rhythmic motifs borrowed from the master’s own catchy tunes. ICP keeps changing, at its own measured pace, but it remains one of the best, funniest, and most resourceful groups in contemporary music. Plus, the gig is free. Monday, November 26, 7 PM, Preston Bradley Hall, Chicago Cultural Center, 78 E. Washington; 312-744-6630.