Concert of Hector Berlioz at the Cirque Olympique, “L’Illustration”, 25 January 1845. Bibliothèque nationale de France, Gallica, via Wikimedia Commons (public domain).
Looking at an orchestra from the stalls you see an arrangement that seems obvious: violins on the left, cellos on the right, winds in the middle, percussion at the back. It is not obvious at all. It is a recent choice, the alternative survived until recently, and it changes what you hear.
For almost all of the nineteenth century and until the 1930s the standard layout was different: first violins on the left and second violins on the right, facing each other, with violas and cellos in the middle. It is called divided, or antiphonal, seating, or the “European” arrangement. The reason is purely musical: in classical and Romantic music the first and second violins answer each other continually, they pass fragments, they imitate at a distance of one bar. With the two sections on opposite sides, that dialogue is heard as dialogue. With the two sections side by side, it becomes a single sound.
The change comes in the first half of the twentieth century, in the English-speaking world and then everywhere. The reasons are practical and worth stating without mythology. The first is recording: with microphones and later stereophony it was convenient to compact the high strings on one side, because the sound turned out more homogeneous and easier to capture. The second is balance in a large hall: the violins on the right play with their soundboards facing the back of the stage instead of the audience, and in an auditorium of two thousand seats they are heard less. The third is the convenience of rehearsals: two adjacent sections tune to each other faster and play together with less work.
The price of those three conveniences is that part of the writing becomes invisible. In the symphonies of Beethoven, Brahms and above all Mahler there are passages built on the stereophonic effect between the two groups of violins, and with the modern arrangement that effect vanishes. It does not sound worse: it sounds like something else. Several conductors, in recent decades, have gone back to the divided arrangement for precisely this reason, and anyone who listens to the same piece in both versions hears the difference in the first minute.
The rest of the geography of the stage has an equally concrete logic. The double basses sit at the back and up high because low sound takes longer to define itself and needs space behind. The woodwinds sit in the centre because they must be heard by everyone, since they carry much of the solo lines. The brass sit behind because their projection is directional and extremely powerful, and placed in front they would cover everything. The percussion are at the back for the same reason, with the addition that the timpani need a rigid surface underneath so as not to lose definition.
Then there is a rule nobody writes down and everyone applies: the risers. Raising a section by twenty centimetres changes its relationship with the audience more than any dynamic marking in the score. In many halls the balance problems that the conductor tries to solve in rehearsal are in reality problems of elevation.
The reason it is worth knowing, as a spectator, is that all this is visible before the concert even begins. Just look at where the second violins are when the orchestra comes in. If they are on the right, facing the firsts, that evening someone decided that the dialogue inside the score matters more than convenience. It is information about the reading you are about to hear, and you get it free, from your seat, while they are still tuning.