Here is an example of Schumann’s bad orchestration. The beginning of the second movement features a lovely melody in octaves for the first violins, a sustained, syncopated accompanimental texture for the second violins and violas, and a bass line in contrary motion to the melody in the cellos and basses. Here are the problems:
1. Octave doubling of melodies is great on the piano, but ineffective in the violins, especially in the relatively less expressive middle of the violin register, where this melody lies. The octave doubling adds little weight and makes the melody a tiny bit out of tune, which is sometimes welcome, as it warms up the sound, but not here, where it is essential that the first violins, who are all on their divisi lonesome, hold their own against all of the second violins, violas, cellos, and basses.
2. The second violins and violas are trying to duplicate the effect created by a pianist’s right foot on the sustain pedal. Maybe Schumann congratulated himself on finding such a subtle rythmic expedient to represent the piano’s pedal, but he shouldn’t have been trying to represent the piano’s pedal at all, the orchestra has plenty of ways of its own to create sympathetic vibrations. Also, and most damaging, the ensemble is gonna be a huge problem. Even the finest players in the best orchestras are going to be tentative here, they are not going to be as comfortable finding the beat and coming in properly, with well co-ordinated ensemble as they could be. And all for nothing. Plus, this passage is likely to consume valuable rehearsal time.
3. All the cellos and basses playing a kind of mirror image of the first violins (who are not in a brilliant register, or in a great violin key [the key here is E-flat Major]) are more than a match for the first violin section; there is a danger of a bottom heavy sound, and in any case, the melody should predominate, as this is a homophonic texture.