The Brodsky Quartet, playing in Dublin tomorrow, try anything from chamber music to Elvis Costello. It's the same 12 notes, just in a different order, they tell Arminta Wallace

Superstring theory is a hot notion in contemporary physics. According to this theory, everything in the universe, from a hippopotamus to an MP3 player, a chunk of bog oak to Roy Keane - is composed of tiny vibrating strings. Since the patterns of vibration vary, there are variations in the resulting electrical charges - which is why you can't get blood from a chunk of bog oak, or plug Roy Keane into your computer - but the starting-point is always the same. Vibrations. Not good vibrations and bad vibrations; not high art vibrations and low art vibrations.

Just vibrations. Superstring theory bears a striking resemblance to the way in which the musicians known collectively as the Brodsky Quartet produce music. The strings vibrate, and out pops a critically acclaimed recording of Shostakovich string quartets. They vibrate again, and this time it's chamber music by Otto Respighi. Or a song cycle by Elvis Costello. Or a chunk of Beethoven. As the group's viola player, Paul Cassidy, likes to point out, "it's the same 12 notes, but in a different order".

On a freezing February afternoon the quartet is ensconced in a cosy basement at BBC Broadcasting House in London, doing a publicity blitz for two new albums which rearrange the same 12 notes yet again. The first of these albums opens with a lively version of Elvis Costello and Cait O'Riordan's song, My Mood Swings, complete with Costello's inimitable vocals - and a note by him in the CD booklet which reads, "When the quartet asked me for My Mood Swings, I thought: they're mad. That song can never work with string quartet. Should have known better, really . . ."

The second album features quartets by Tchaikovsky - and programme notes which stress the music's "restless chromatic modulations and bold soloistic gestures".

For many "classical" musicians this would be a matter of chalk and musical cheese, but as two out of four Brodskys emerge from the depths of the recording studio - violinist Ian Belton and cellist Jacqueline Thomas having gone off in search of sandwich-type sustenance - it becomes obvious that as far as they're concerned, the two albums are of equal artistic importance. Moodswings, as viola player Paul Cassidy explains, is an album of songs for human voice and string quartet; a combination which has intrigued the Brodskys ever since they recorded The Juliet Letters with Costello just over a decade ago.

But it's more than that. It also puts the finishing touch to an innovative educational project which has seen the quartet working closely with six secondary schools across England over the past three years. "The initial idea", says Cassidy, who came up with it, "was to mix music, art and English classes. Mix them up; and try to force the kids to write songs for string quartet and voice. There was also a whole side to it where they were invited to do stage design, CD cover design, clothes for us to wear at concerts - anything that fired their imagination or creativity."

The Brodskys did an artistic blitzkrieg in each school, moving in with a back-up team which included a singer, a designer, two composers and a writer. All other classes were put on hold, and at the end of a week, songs began to emerge from the haze of ideas and confusion.

"Many of the kids had no idea about music," says Cassidy. "They were real beginners. But we came away with over 100 songs."

One composition from each school was eventually chosen for the CD, and juxtaposed with songs by what Cassidy terms "slightly better-known songwriters" - Sting, doing a new version of Until . . . ; Ron Sexsmith bouncing his way through Dumptruck; Costello's whimsical delivery of Randy Newman's Real Emotional Girl. The result is a voyage through a mad variety of musical universes which ought not to work, but somehow does. Working with untutored teenagers seems to have inspired rather than depressed the quartet.

"They came up with a wonderful mixture of styles," says first violinist Andrew Haveron. "Styles that don't, perhaps, automatically enter into our wishlist of the sort of music we want to play. But given the nature of the project, we were encouraging them to do whatever they wanted to do." He laughs. "We didn't get any rap, unfortunately. It's a shame. We got just about everything else, though - from French chanson through to a bit of ska . . ."

Unusual collaborations, of course, are not unusual for the Brodskys, who have worked with singers of every vocal shape and colour, from the cool mezzo of Anne-Sofie von Otter through Meredith Monk's wordless howls of misery to Björk's . . . well . . . how would they describe Björk, who, on Moodswings, delivers a majestic version of the song she co-wrote with cinema director Lars von Trier, I've Seen It All?

"An extraordinary artist and extremely professional," says Haveron. "She has written these amazing songs and she lets us do what we want with them and goes with whatever happens. She just surfs our sound. When we did the live concerts with her in Islington in 1999 she loved the risk of being somewhat naked - no electronics, no microphones, all just pure acoustic experience."

The concerts in question have acquired almost legendary status in London musical circles, thanks partly to a slew of gobsmacked reviews, partly to the unprecedented mixture of what Haveron describes as "classical audience, the regular Islington crowd and heavy-duty Björk fans - whom you couldn't begin to describe".

The Brodskys have come a long way since, as precocious teenagers, violinist Ian Belton and Jacqueline Thomas initiated a group called the Cleveland Quartet - only to discover that the name was already taken by a world-famous outfit from Ohio. At music college in Manchester they met Derry-born Cassidy, and decided to adopt the name of the iconic Russian violinist Adolf Brodsky, a pioneering figure in the city's musical history. His original Brodsky Quartet, formed at the turn of the 20th century, was among the first to play Tchaikovsky's music for string quartet - neatly turning the new album into a direct link with Brodsky history. True to Brodsky form, the quartets explore an unusual mood in Tchaikovsky's music - passionate and muscular, but totally lacking the sickly sweetness which characterises his more popular works.

"The Tchaikovsky quartets aren't on the A-list of repertoire," says Haveron. "I mean, apart from Number One, with its famous slow movement - but I personally feel the other quartets are better pieces of music. They may not have such a catchy tune in them anywhere. I personally believe they do - but history doesn't agree with me."

"They're real heart-on-sleeve, that's for sure," adds Cassidy. "When you've played one of them, you know you've given a concert. They're 40 minutes long, and each one is a tour de force."

The Brodskys won't be performing Tchaikovsky when they play at the National Concert Hall in Dublin on Saturday - their first performance in this country for almost 15 years. What are they going to play, and how would they describe the programme?

"Some interesting examples of what the quartet can do," says Haveron. "The two main pieces are the quartet by Ravel, and Samuel Barber's quartet - which contains The Adagio."

What, Barber's Adagio, usually heard in luscious multi-stringed arrangements? "Yes. That's where it comes from - it's the second movement of his string quartet. It's just that people aren't used to hearing the outer movements." Does the highly familiar, almost hackneyed nature of the piece demand a particular approach from the group? "Well," says Haveron, "We're not the 100-strong string section of the Berlin Philharmonic, you know? So - as usual with a quartet - it's more intimate, and perhaps more powerful."

"And also," chips in Belton, who has returned from the sandwich search, "it has to be done very well. Whenever you play that piecethe cry goes up from whoever is in charge - or, at least, when I'm in charge - 'free bowing'. Which means that everyone changes the bow at a different time so that it isn't obvious. But as we're all playing different parts, you have to do it really well. Otherwise those famous long lines just . . . well, stop."

The programme opens with Metro Chabacano by the Mexican composer Javier Alvarez, who has written many pieces for the Brodskys. "It's a lovely little piece - minimalistic, I suppose, if you have to call it something," says Cassidy.

"A soundscape," declares Haveron. "I think that's a good word for it. A train ride across Mexico. And the other piece is by Javier's teacher, Mario Lavista. It's called Reflejos de la Noche - Sounds of the Night - presumably a hot Mexican night, with some very nasty insects flying around. It's written all in harmonics, so it's a very unusual sound world. You won't hear something like that very often. And I think we're throwing in a bit of Gershwin as well."

All this, and a masterclass in the afternoon into the bargain? Well, not quite. "I believe," says Cassidy, "it has become something slightly other than a masterclass. It will be more like a talk. A discussion. We will appear on the stage at around 3.30, probably do a little bit of playing, talk about what we do for a living and . . . invite a bit of debate? Questions?"

The Brodsky creative strings are, it seems, vibrating again - and if past form is anything to go by, anything could happen. He looks inquiringly at Haveron, who nods, and Belton, who bursts out laughing. "Hopefully there will be people to ask questions," he says. "Will you come? Bring a friend . . ."

The Brodsky Quartet performs at the National Concert Hall in Dublin tomorrow at 8pm. For further information on the afternoon session, phone the hall at 01-4170077. The albums Moodswings and Tchaikovsky Quartets are available from Brodsky Records