Wigmore Hall, London. As the Quatuor Ebène plays the last notes of its final piece on the concert, the standing-room-only audience’s applause is immediate and overwhelming. The crowd response brings the Ebène back to the stage several times, but vanishes quickly when the musicians return to their seats, signaling the hoped-for encore.

But what’s this?

All four players rise out of their seats and start singing “Someday My Prince Will Come” in perfect harmony. Laughs and gasps from the audience are followed by delight as the quartet sits down again, picking up instruments and getting into a jazz version of the popular jazz standard.

The audience’s surprise is understandable: after all, it was only minutes before that the classically trained young French ensemble had played the exquisite and enigmatic Fauré quartet.

This “other side” of the Ebène—the playful take on pop and jazz with some improvization in the mix—shows up in encores at the quartet’s concerts around the world. While the critics are charmed by the versatility of a chamber ensemble prepared to segue from Haydn directly into an arrangement of surf-guitar king Dick Dale’s “Misirlou,” the theme from Pulp Fiction, it’s the Ebène’s classical side that has so far attracted the most attention.

The group’s first album for Virgin Classics featured three masterpieces of the French quartet literature by Debussy, Ravel, and Fauré. It won the 2009 Gramophone award for Record of the Year. They’ve also received plaudits for discs of Haydn and Brahms, and are regulars in leading concert halls in Paris, London, and New York.

In short, this is a multi-talented, multi-tasking quartet on its way up.

Speaking to the group in their hotel lobby the morning after a recent Wigmore appearance, I am struck by their openness and seriousness, though not without some sibling-like joking. The four met ten years ago at the music conservatory in Boulogne-Billancourt, a Paris suburb whose prosperity, according to violist Mathieu Herzog, accounted for the unusually high quality of the school. Herzog says the faculty interest in encouraging chamber music was equally unusual, at least in France. He and first violinist Pierre Colombet met in a chamber-music ensemble and decided to put together their own quartet.

“For me, the quartet has something like the perfect balance between orchestral and soloist roles,” Herzog says. Second violinist Gabriel Le Magadure joined a year later, followed a few years later by cellist Raphaël Merlin.

“We needed time to find the perfect balance between four people,” Herzog says.

Individual studies soon took a backseat to the intense work of the quartet. “From the beginning we practiced several hours a day, six or seven hours,” Herzog recalls. “Work, work, work.”

The musicians studied with the Ysaÿe Quartet, who encouraged them to enter the Bordeaux quartet competition. “I’m not sure we were a good string quartet when we did this competition,” Herzog says.

But, at any rate, the players were hungry for success. “We were just like lions—we were wild!” Le Magadure says with some glee.

The result? The quartet came in second—no first prize was awarded.

At the competition, the chamber-music guru Gábor Takács-Nagy, who served on the Bordeaux jury, liked what he heard. Soon the Ebène were heading to Geneva to study with him. “We discovered the Hungarian way of seeing the music,” Le Magadure says. “A Hungarian guy doesn’t play like a French guy, I can tell you.”

Additional non-French influences came from Eberhard Feltz at the Hanns Eisler Hochschule in Berlin. “Together [Takács-Nagy and Feltz] were perfect for us,” Le Magadure says.

In 2004, the musicians won the prestigious ARD competition in Munich, taking first place and five other prizes. “We decided to win,” says Herzog, clearly the group’s motivational coach.

“You decided to win,” Le Magadure jokes. The morning after their victory, Quatuor Ebène had a fistful of engagements and its members’ lives had changed immediately.

It seems only fair to say that the Ebène’s highly individual, intense style perplexes some listeners, but I find that the ensemble can create a musical atmosphere like few other quartets, an ability that serves it particularly well in Brahms and in the French repertory. The players speak admiringly of the equally committed interpretations of the now-disbanded Lindsay Quartet. “You had the emotion in your hands with these guys in concert and that’s so rare,” Colombet says.

The Ebène’s relentless rehearsal schedule is going to ease at least for a while in 2010, though at press time the group had US dates on its schedule, with first violinist Colombet expecting his first child later this year (his wife is pianist Akiko Yamamoto, who plays the Brahms Piano Quintet on their recent disc.) “We can’t rehearse until 11 pm just for the pleasure anymore; now we will have to make rules,” La Magadure says.

There are rules in the classical-music world, one being that performers should shun crossover projects until they are really established. The Ebène are happily ignoring this rule. The group’s next Virgin Classics recording, scheduled for a fall release, is going to be a collection of crossover arrangements from its “other side.”

Surprisingly, no single player is responsible for these arrangements; instead, the pieces are put together collectively. “We begin from zero, and we don’t write first; we just memorize,” Colombet says.

Rehearsing is as elaborate as it would be with a standard classical work, Herzog says. “Pierre can say, ‘Oh, I think this harmony is not good, please try this, change this note.’ Okay, but the feeling’s not good. Ah, now we have to make the new dynamics. It’s really like rehearsing a string quartet.

“The only difference is that we can imagine what we want.”

And if arguing about dynamics and interpretation is exhausting in Beethoven and Brahms, it can also be just as grueling in their collaborative arranging process. But it’s complementary to their classical work, Colombet says, “because we are absolutely not the same kind of musician, but we can find the quartet homogeneity in any work.”

Jazz great Wayne Shorter’s classic “Footprints” and Charlie Chaplin’s popular “Smile” are some of the pieces the group is planning to include on the new disc. The players can’t discuss everything that will be included, but I do ask if they’ll be singing on the new disc.

“Yes!” the four reply in unison.

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