How did Smetana and Dvořák's music sound to their own ears? Anima Eterna Brugge and Jos van Immerseel think they know. Having started as experts in historically informed performances of early music, they have made a mission of researching the instruments and orchestral layout of the period of everything they perform. They have been spending the last few years taking that approach forwards in time through the romantic movement towards the early 20th century.

The answer to the question turns out to be "quite different from what you're used to" – at least, that is, when performed within the acoustic wizardry of the Concergebouw Brugge, built in 2002 and now the home of Anima Eterna. It was clear from the first notes of Smetana's Vltava, the long skirl of two flutes glowing brilliant sunshine above the river of strings which ripples swiftly, but peacefully, rather than with the thunderous growl which a more modern orchestral sound would give. Spreading across the stage of cellos and basses also has a strong effect, giving the sound a broad base rather than providing a single platform of low notes.

The Concertgebouw's acoustic turns convention on its head by using hard surfaces throughout, but breaking up the sound by forming almost every space in walls or balconies into pseudo-random geometric patterns. The effect is to generate a great deal of warmth and richness of reverberation combined with a relatively short reverberation time – in other words, you hear lots of string timbre without it turning to mud. Not all is perfect, though: clarinets were far dimmer than flutes, and I lost the harp in Vltava altogether.

Immerseel's approach to the Dvořák New World Symphony is a calculated one: he is allowing every instrumental sound the space to breathe and be properly heard. This is partly a question of orchestral balance: with the strings softer than usual, each woodwind phrase comes through with clarity. It's partly the string sound itself, with the notes easier to hear individually. And it's partly a question of tempi: Immerseel's “New World” is one of the slowest you'll hear. And there were plenty of delights: the famous cor anglais solo of the second movement shone through with as much beauty as I can remember. Throughout the evening, the flautists were outstanding, a mixture of wooden and metal instruments producing sweetness of tone and lifting the whole orchestra.

There are compromises, of course. The principal one is that gut strings and slow tempi cannot produce anything close to the sheer thrill and attack generated by a more conventional modern symphony orchestra in full cry. So while we could hear the structure and ebb and flow of Dvorak's fourth movement with complete transparency, the result was far less of a passionate roller coaster ride than usual: a feast for the intellect rather than for the senses.

After the interval, however, there were no problems of attack from the thirteen additional brass players standing in line above and behind the orchestra for the military fanfare that opens Janáček's Sinfonietta. It's a gloriously bold movement, scored for brass only except for a prominent timpani part, and if Anima Eterna's brass didn't give it the most precise rendering, they producted plenty of verve and energy, with the brass instruments sounding gloriously rich. The second theme was played with a swagger – a touch of swing, even – before returning to the solidity of the military opening theme.

A quirky set of figures on muted trombones accompanies the opening of the second movement Andante before this settles into a rhapsodic string passage, followed by a mercurial set of variations in which the military brass is never far away. That mercurial sense continues for the rest of the work: bold themes are passed by turns between each instrument group in the orchestra, with everyone getting their chance to shine until the last movement, which has opened on a melancholy note, ends with a return to the opening fanfare. As in the whole of this concert, the distinguishing feature was the clarity and beauty of individual instrumental sound. The multiple colours of the Sinfonietta brought a satisfying close to an evening of unusual exploration of these familiar great Czech works.