“I’ve always wanted the string quartet to be vital, and energetic, and alive, and cool,” David Harrington, violist and founding member of the Kronos Quartet, once said, “and not afraid to kick ass and be absolutely beautiful and ugly if it has to be.

“But it has to be expressive of life,” he continued, “to tell the story with grace and humor and depth. And to tell the whole story, if possible.”

Harrington’s vision has been realized. Kronos has redefined the string quartet. Sure, they play classical music, but they also play arrangements of Thelonious Monk and Icelandic rockers Sigur Ros. And if you think Jimi Hendrix’s music can’t get any more psychedelic, check out Kronos’ spacey takes on “Foxy Lady” and “Purple Haze.”

The Grammy-winning group has performed with the likes of Tom Waits, David Bowie, Nine Inch Nails and DJ Spooky; they’ve collaborated with renowned composers like minimalist Philip Glass. Kronos has also composed several film soundtracks including Alejandro González Iñárritu’s 21 Grams, David Byrne’s True Stories and most notably, Darren Aronofsky’s Requiem for a Dream, which makes the hairs on your arms stand up involuntarily.

In fact, Kronos – Harrington, John Sherba (violin), Hank Dutt (viola) and Jeffrey Zeigler (cello) – have crossed over into just about every musical genre, which is one of the reasons why they continue to achieve mainstream success. Musically, you never know where Kronos will go next. Their ever-expanding versatility is evident in its catalog of more than 45 albums, which includes the music of Bollywood, Romanian gypsy music and the music of Bill Evans.

“What I have wanted to do with my life is to expand that foundation that the string quartet got from Haydn, Mozart, Beethoven and Schubert, and bring more interesting voices, interesting perspectives, interesting personalities into this world,” Harrington told The Rumpus.

Kronos’ live performances are just as unconventional as its repertoire. Over the years, they’ve employed amplifier feedback, irregular time signatures and have even dressed in all-black spandex.

On Friday at Sunset Center the eccentric quartet will perform George Crumb’s avant-garde Black Angels: Thirteen Images from the Dark Land, the only time the quartet will play the piece on its worldwide tour. The experimental work – a response to the Vietnam War featuring bowed water glasses, metal thimbles, spoken word and electronic effects – has an especially deep meaning for Harrington: In 1973, after hearing it for the first time, he was inspired to form Kronos.

“It was a startling, scary experience to hear that music,” he said more than 15 years ago, “and it was a kind of experience that maybe you have once in a lifetime where all of a sudden I knew what I was going to do, and what I wanted to do was play that music.”

Black Angels – divided into three segments: departure, absence and return – is a dark interpretation of the battle between good and evil; a piece from it was even used in the original Exorcist.

Friday’s program also includes originals composed and arranged for Kronos by Frangiz Ali-Zadeh, Bryce Dessner, Ram Narayan and Aleksandra Vrebalov.

In addition to touring and recording, the quartet also runs a nonprofit in San Francisco called the Kronos Performing Arts Association. Its mission is to mentor and encourage other artists to redefine the string quartet experience – as if their boundary-crossing performances weren’t quite encouragement enough.

THE KRONOS QUARTET performs 8pm Friday, April 23, at Sunset Center, San Carlos at Ninth, Carmel. $42, $48, $57. 620-2040.