What in the world is SoundBox?

That very question was on the minds of the fans who lined up Saturday night, along Franklin Street, for a first glimpse of San Francisco Symphony’s new performance space and music series. “Excuse me,” I overheard a woman a few feet behind me ask, “do you know what this is that we have tickets for?”

“Not really,” replied a man’s voice, “but it’s supposed to be really cool.”

With virtually no advertising aside from street graffiti stencils, social media and word of mouth, SoundBox certainly arrived with an air of mystery. Was it a club? A chamber concert? Whatever it was, the majority prediction had already framed it as the Symphony’s attempt to attract younger people to classical music, a goal toward which the world has seen plenty of awkward or even downright embarrassing attempts, by other outfits: symphonic renditions of Grand Theft Auto, incessant string-quartet tributes, and even a Sir Mix-a-Lot twerkfest with symphony orchestra.

And yet amidst these predecessors, SoundBox succeeds on every level, both demographically and artistically. The brainchild of Symphony music director and conductor Michael Tilson Thomas, it’s simultaneously a concert series, warehouse party, experimental workshop, nightclub and sound immersion. It takes classical music from all eras and presents it squarely in the modern day, with cocktails, freedom to wander about and phone and tablet use encouraged. It’s the most comfortable way for many to experience classical music. It’s also the perfect date night. And yes, it’s the coolest thing on the block.

On Saturday night, after entering, patrons who’d paid $25 per ticket crossed a catwalk over a desert landscape while ambient thwonks and whooshes filled the entryway. The cacti, bushes and shells below, wired for sound, shook and rattled at the hands of three musicians performing John Cage’s Branches. These sounds also resonated throughout the 7,600 sq.-ft. main room, which contained a bar at one end, a stage on two sides, seating at low tables in the center, high tables around the perimeter, three large projection screens and atmospheric blue lighting cascading upward along exposed concrete and steel beams, all of which rose to an incredible 50 ft.-high ceiling.

Such was the visual transformation of Zellerbach Rehearsal Hall A, essentially the bare-bones underbelly of Davies Symphony Hall. Acoustically, the room required some transformation, too—as Tilson Thomas noted in his introduction, it’s “one of the deadest places in the world to hear music.” Enter Meyer Sound’s Constellation system, with 25 microphones and 85 speakers, which provided a complete retuning of the room’s acoustics at the click of a laptop. Every piece received a different acoustic treatment, from the cathedral to the recording studio, to fit its sound.

And then there was the program, which in its sheer variety had something for everyone. Curated by Tilson Thomas, the evening began in 14th-Century Spain with “Stella Splendens in Monte” from the Llibre Vermell de Montserrat, sung by choir members entering the back of the room and walking through the crowd. From there, the night straddled the traditional and the avant-garde without once seeming eclectic for eclecticism’s sake—not even when Ravel’s Introduction and Allegro (performed to perfection before a projection of Monet’s Waterlilies and highlighted by harpist Doug Rioth’s breathtaking cadenza) came immediately on the heels of the Steina film Voice Windows, featuring wild vocal calisthenics by Joan La Barbara.

Symphony communications director Oliver Thiel told me before the program that “we wanted to see if we could get a crowd that wouldn’t go to Davies,” and to that end, each piece selected by Tilson Thomas provided a window in for fans of different music. Electronic producers or DJs would have found a great kinship in the quintet performance of Steve Reich’s rhythmic, repetitive Music for Pieces of Wood. Any fan of art-rock indie bands like Deerhoof or Dirty Projectors would have thrilled at the choreographed stomping and yelping of Meredith Monk’s Panda Chant II. Even Edgar Varèse’s Intégrales, an exercise in bulbously despairing trombones, off-time cymbal crashes and a mutiny of clarinets, contained the type of furious drums and horn stabs that are so common in current hip-hop production.

As if the atmosphere couldn’t have been any more casual, during one intermission, a choir member walked up to me and handed over his black folder of music. “So, they told us to walk out into the audience and hand out our sheet music, so people could sing.” I looked at him quizzically. “After a few cocktails,” he urged, “it’s really not that hard.”

His quick smile let me know that he was joking, and we shared a laugh, but the fact that his proposal was entirely believable speaks to the anything-goes nature of the night.

At the end of the final intermission, signaled by Reich’s Clapping Music in surround sound instead of blinking lobby lights, Tilson Thomas conducted Monteverdi’s Magnificat, from Vespro della Beata Vergine. One of his self-described “desert island” pieces, it fit the room in ways that it wouldn’t have fit at Davies. And as the beauty of the choir’s soloists washed over the crowd, I noticed a spilled drink at Tilson Thomas’ feet, which is just about the best image I can conjure for the working juxtaposition of the night.

And how did it feel for Tilson Thomas, test-driving the premiere of SoundBox?

“There are a lot of different steps to go through in making something like this happen, and there are times, when you’re in the middle of it, when you think it’s never going to happen,” the conductor told me, just after stepping from the small, 18-inch high stage and mingling with the crowd. “So it was tremendously rewarding to feel the response of the audience—many of them who’ve probably never heard any of these pieces before—and to have this kind of spontaneous reaction to what classical music really can be.”

SoundBox returns Friday and Saturday, Jan. 9-10. Tickets go on sale Monday, Dec. 15. For more info., see SoundBox’s site.