YOU might not expect to find a polished young ensemble like the Parker String Quartet playing music by Beethoven, Bartok and Ligeti — or collaborating with ensembles like Las Rubias del Norte, which specializes in Latin American folk music — in the no-frills back room of a Brooklyn bar. But the group spent this season as the resident quartet at Barbès, a Park Slope bar that regularly presents classical performers in a schedule otherwise devoted to jazz, pop and world music.

Barbès is not alone. In the last few years some of the most memorable performances I’ve heard have been in places like it. There have been works by Cage, Xenakis and Louis Andriessen in the Spiegeltent at the South Street Seaport; new music presented by the MATA Festival at the Brooklyn Lyceum, a converted bathhouse in Park Slope; and wildly disparate versions of Terry Riley’s “In C”: a bracing chamber version in the Serial Underground series at the Cornelia Street Café in Greenwich Village and an electric chamber and indie rock hybrid performed in the Darmstadt new-music series at Galapagos, a performance space and bar in Williamsburg, Brooklyn.

Joe’s Pub in the East Village has become a favorite haunt of classical players; and the annual Bang on a Can Marathon and ensembles like Ethel, the amplified string quartet, have made the Winter Garden at the World Financial Center in Lower Manhattan an unlikely avant-garde hub. The Issue Project Room and, more occasionally, Zebulon and Monkey Town, all in Brooklyn, have been eliminating the borders among independent rock, avant-garde jazz and classical new music.

On Sunday evening Le Poisson Rouge, a new club, opens on the site of the old Village Gate, on Bleecker Street in Greenwich Village. Its eclectic schedule will include classical music, old and new, amid rock, jazz, world-music offerings and installments of the JVC Jazz Festival this month.The proprietors of Le Poisson Rouge are classical musicians: Justin Kantor, 29, a cellist, and David Handler, 27, a violinist and composer. They began dreaming of an alternative performance space in 1999, when they were students at the Manhattan School of Music and had grown bored with the formality of the standard concert setting — what Mr. Handler calls the “preacher and congregation seating arrangement” — and alarmed at the high cost of tickets. At Le Poisson Rouge most classical performances will be in the round, and bar receipts will help underwrite the programming.

“Alcohol is our patron,” said Mr. Kantor (who, I should add, was a student in a music criticism course I taught at New York University in 2004).

Gutted and rebuilt — partly to keep noise from disturbing the neighbors, as it has in the club’s past incarnations — Le Poisson Rouge has a flexible concert room that, depending on the seating (or standing) plan, can accommodate 200 to 800 listeners. With acoustics and a high-tech sound system by John Storyk, whose previous projects included Jimi Hendrix‘s Electric Lady Studios and Jazz at Lincoln Center, Le Poisson Rouge is for the moment the spiffiest of the alternative concert rooms. But it will soon have competition: both Galapagos and the Issue Project Room are moving to newly refurbished spaces in the Dumbo section of Brooklyn.

Le Poisson Rouge’s trump card is likely to be its programming. Ronen Givony, 29, whose adventurous Wordless Music series has won a large, enthusiastic (and young) following over the last two seasons by bringing together classical performers and indie rock bands, is overseeing the classical and electronic performances. Brice Rosenbloom, 34, best known for his programs at Makor and the Knitting Factory, is programming the club’s jazz and international music.

Le Poisson Rouge’s first classical offering, on Tuesday, will be a piano recital by Simone Dinnerstein, who will play Bach’s “Goldberg” Variations and George Crumb’s “Little Midnight Music.” Mr. Givony’s early plans also include evenings by the new-music pianists Kathleen Supové and Jenny Lin; Michael Riesman playing piano works by Philip Glass; and Signal, a new-music orchestra, playing pieces by Steve Reich; and a staging of Monteverdi’s “Incoronazione di Poppea” by OperaOmnia.

“Wordless Music was basically monthly, and I always had more proposals than I could accommodate,” Mr. Givony said. “I want to use this to do all the cool things I’ve wanted to do.”

So while the big guns in the classical music world fret about luring new — especially young — audiences, enterprising club owners, performers and artist managers are creating a thriving underground arts ecology. The attraction of these informal events has not been lost uptown. Lincoln Center now offers postconcert recitals and even full-fledged productions (like I Fagiolini’s “Full Monteverdi” last summer) at the Kaplan Penthouse, where concertgoers can sip wine during performances. And the Brooklyn Academy of Music sometimes links concerts in its upstairs BAM Café with offerings in its main hall.

“I don’t look at this as a way to get people into concert halls, and I think that’s the wrong way to view it,” said Patrick Hammond, who put together a circuit of bars, clubs and coffeehouses for Concert Artists Guild, an organization that manages the young musicians who win its annual competitions. “We’re just creating another way of experiencing the music.” “You’ve seen the crowd at Barbès: it’s old, young, died-in-the-wool classical listeners and people who wouldn’t know Bach from Beethoven,” he added. “This great music is what we have, and we need to put it out there in as many ways as we can. And there are kids coming out of conservatories now who don’t see it