Yesterday the BBC Scottish Symphony Orchestra announced the line-up for its third annual Tectonics festival, which takes over Glasgow's City Hall and Old Fruitmarket for the weekend of May 1-3.

Once again, it is like no other orchestral brochure you're likely to pick up - unless you happen to be wandering the concert halls of Reykjavik, Adelaide or Tel Aviv. The common denominator between these disparate cities? BBCSSO principal guest conductor Ilan Volkov, who launched the Tectonics concept in Iceland in 2012 and whose disregard for classical orthodoxy is genuinely shifting the parameters of what a 21st century orchestra can and will do.

Co-curator for Tectonics Glasgow is the producer Alasdair Campbell, a man whose encyclopaedic enthusiasm for the Scottish underground music scene adds some wild collaborations to the mix. The weighting of this year's programme falls more towards small configurations of eclectic improvisors than heavyweight orchestral music, with Ben Patterson, Peter Brötzmann, Rhodri Davies, Heather Leigh and Hild Sofie Tafjord among the featured performers. Whether that balance feels right on the weekend remains to be seen. What's already clear is Tectonics's capacity to engage artists who otherwise avoid the hierarchical nature of orchestras.

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Take the experimental Welsh harpist Rhodri Davies, who studied classical harp and spent several years freelancing with major UK orchestras. At 40, having drifted into London's improvisation circles, he decided to quit the orchestral world altogether. "Most of my improvising contexts are smaller groups that work in a more collective way than orchestras do," he explains. "I found the hierarchy thing stifling, so I decided to call it quits." A year later he got a call from Volkov asking whether he would perform in the BBCSSO John Cage centenary concert at the Proms. "Because it was him, and because of the repertoire, I agreed to do it. If anyone can break down the weight of orchestral tradition it's Ilan. I hope the classical music world is listening to what he and Tectonics are doing."

In terms of flouting expectations, the same could be said for Davies himself. The harp has about as many historical trappings as an orchestra: think of Orpheus, who played the instrument so beautifully that he charmed Hades himself. The noises that Davies gets out of his instrument are not always beautiful. The first time I heard him was at an experimental music festival in Cardiff, where he pulled brilliantly abrasive sounds out of a traditional Welsh clarsach. He thrashed and tugged and hammered at the strings. Fragments of sweet tunefulness emerged from the clatter, but these were routinely and gleefully shattered. Davies has gone as far as setting fire to harps for sound-art installations; when he presented that particular project to a harp congress, people booed and walked out.

Davies's hope is that contemporary music will build an audience as broad and eclectic as those interested in contemporary visual art. "Maybe galleries are easier because you can walk away. Part of the problem is the concert-hall environment, way too much like a church." Roll on Tectonics, much of which happens on the floor of the Old Fruitmarket with the audience wandering among the artists.

But for many, the big excitement of this year's programme will be music so delicate and beautiful that it pins you to your seat and makes you hold your breath for fear of interrupting the exquisite balance. Eliane Radigue is a pioneering electro-acoustic composer who turned 83 last week. The trademark sound of her music is slow, subtle and hypnotic: she's a committed Buddhist and her art is steeped with the meditation she practises daily. It is sound about sound, music that magnifies the elements of itself into minute and wondrous detail. In the 1970s she began working with synthesisers, especially the ARP 2500, and in 2004 she made a radical decision to write for live musicians.

"I was so excited when she started composing acoustic music," says Davies, who has worked with Radigue on several pieces since meeting her in 2011. "She used to play the harp, her son plays the harp and she honours the great French harp tradition. She has a wonderful way with the instrument." Her electro-acoustic heritage is still there in the drones and harmonics of her instrumental scores - sometimes she uses electronics so subtly and gradually that you don't realise they're there until they've cross-faded away. Davies describes Radigue as a "vibrant and rigorous person" and an "incredibly serene presence. She's a true inspiration."

Tectonics 2015 is at Glasgow's City Halls and Old Fruitmarket, May 1-3