Arditti String Quartet / Ades, Queen Elizabeth Hall, London, **

Each half of this well-attended Queen Elizabeth Hall concert opened in true Arditti String Quartet fashion with a solid 20th-century classic. Or, solid, at least in the case of Alban Berg's String Quartet Op 3 – his 1910 graduation piece from the demands of four years of study with Schoenberg.

After 90 years, it remains a pretty exacting structure to follow in its own right: dense with motivic transformations, turbidly chromatic in harmony and softened at the edges only by gestures of Berg's lingering Romanticism. In comparison, Henri Dutilleux's Ainsi la Nuit (1976-77) seemed lightweight indeed – an exquisite sequence of sensitised nocturnal doodles, exquisitely played, but rarely straying far from the darkly suggestive chord with which it begins and ends.

But the programme really revolved around two more recent and far more problematic commissions for the Ardittis themselves. Now 67, Helmut Lachenmann has long since epitomised that radical, not to say agonised, tradition of post-Adorno thought in German music forever struggling in a world of consumerist standardisation to attain something authentically new through the exploitation of the most extreme means. The trouble is that those very means have by now become almost standardised – the sounds and textures of a typical Arditti concert. Lachenmann's String Quartet No 3 ("Grido") duly opens with piercing harmonics and tremolo scurryings, later running into an episode of excruciating, heavy scratching, inviting the players to hiss, and so on. One admired the way the composer kept it all going for some 25 minutes without any obvious formal design, but the piece came over as curiously old-fashioned.

Whereas sounding curiously old fashioned seemed the very point of Thomas Ades's Piano Quintet (2000), a large 20-minute sonata structure with the composer himself as elegantly volatile pianist. Or, almost sounding old fashioned, since, a little like Ligeti's Horn Trio (1982), this is writing that seems forever about to resume, or lapse back into, the world of 19th-century chamber music – what most listeners would still regard as "real" music – without ever quite managing to.

So Ades resorts to the most intricate metrical notation in his attempts to simulate the kind of expressive freedom and rhythmic rubato that players of Romantic repertoire have always brought to their interpretations as a matter of course. The fact that this is doomed to fail, and that the composer knows this, is part of the game. But while Ligeti ultimately draws a powerful sense of tragic desolation from the impossibility of reconnecting with the past, not even the dazzling skill that Ades and the Ardittis brought to the quintet could quite convince one that it amounted to more than a postmodern jeu d'esprit.