Not the least remarkable fact about this lunchtime concert was that the performers, as a group, were anonymous.

We knew they were a string quartet from the young orchestra Sinfonia Cymru and that there’s an arrangement whereby orchestra members form smaller chamber groups to play at the Riverfront studio once a month.

But what a stranger might have found astonishing was the sheer accomplishment displayed, especially in a work where the virtuosity taken for granted in ensemble playing is overlaid by additional, if non-flamboyant, dazzle.

This was in one of the so-called ‘Tost’ quartets of Haydn - No 2 in C, Op 54 - named after the brilliant fiddler Johann Tost and exuding rather more than the composer’s customary sparkle, thanks to a first violin part (Rakhivinder Singh) that leads by example but also, as in the sublime slow movement, is prepared to bury itself deeply in the overall mood.

Second violin Simran Singh introduced the totally different bundle of goods that is Beethoven’s Quartet No 11 in F minor Op 95 with the story of the composer’s experience of love unrequited. It made for one of those Beethoven works that barely seems able to contain the force of its own utterances.

It was here, in underlining the contrast between Haydn’s easy eloquence and Beethoven’s deeply personal anxieties, that the players sacrificed some caution and finesse, though not particularly through any imbalance between the two violinists and the equally involved and committed violist (Rhiannon James) and cellist (Jonathan Pether). Sometimes the essential clarity was lost in the heat of several moments.

The four will be part of the full Sinfonia Cymru orchestra currently rehearsing under conductor-founder Gareth Jones for its next short tour of Wales with works by Richard Strauss to celebrate the composer's 150th nniversary.

It will be playing the Metamorphosen for solo strings and the orchestral suite from Moliere's Le Bourgeois Gentilhomme. For the first time in Wales, it is believed, the Moliere music will be accompanied by readings from the play. The orchestra reaches the Riverfront on Sunday March 23.