Few converted chapels can have been put to better use than the Tabernacl in Machynlleth. Its interior resembles a smaller-scale St George's in Bristol, and, while its adjoining art gallery attracts most attention over the year, the summer festival can be relied upon for fine music-making. The Szymanowski Quartet opened this programme with Haydn's Sunrise Quartet, op 76, no 4.

Here the brilliant but mercurial talent of first violin Marek Dumicz proved a little erratic at moments, so things had only just settled into the groove by the time of the last, high-spirited acceleration. But, in the Second Quartet by Karel Szymanowski, there was a real sense of honouring the composer after whom they are named. From the outset, the players captured an emotional pitch at once poetic and atmospheric, the muted strings and ethereal harmonics so sensual as to chime a defiantly exotic note against the chapel's faint echoes of nonconformist austerity.

In the finale, the opening fugue seemed to impose more cerebral parameters on a soul-searching process but, as the temperature was turned up, an almost violent intensity was brought to the chords and folk rhythms. This was a vibrant and wonderfully focused performance.

After the interval, the quartet was joined by Julius Drake for Brahms's Piano Quintet in F minor, a massive work given a positively symphonic force in this interpretation. The combination of Drake's profound musicianship - the long-breathed phrasing and his instinct for harmonic colour that makes his lieder-playing so full of insight - with the coursing young blood of the Szymanowskis made this a powerful experience.

It was all the more moving for defining tiny details of texture and rhythm with the tenderness that must be the essence of chamber music, yet allowing the passion to explode beyond the confines of the medium and reach a more majestic firmament. The embraces at the end suggested that for the performers, too, it had been equally special.