Problem with Two Violins in Unison?

I have often heard anecdotally that one should not score for two violins in unision. From listening it seems like it is hard to tune. But my questions are: is that the only reason? is it always the case? and is it not as much of a problem for viola and cello and bass for some reason?

First, don't cross post the same question into two forums - bad internet etiquette.. :-p

I avoid using only two violins on a single line for pretty much the same reason I don't use two oboes on a single line... the intonation can be a major problem. With three violins the intonation issues seem to become less pronounced; the "edge" is taken off the sound.

This is only my experience, but I've witnessed it firsthand and others have stated the same thing to me as well.

Flint has it dead on.

Generally, and it's important to emphasize generally, two strings in unison don't create as nice a sound. Partially based on the particular quality of the string timbre.

Three will normally sound more like a "group" than two.

However, with excellent players, there's no reason to avoid it at all costs.

The problem then being "yes, but DO I have excellent players?"

I have often heard anecdotally that one should not score for two violins in unision. From listening it seems like it is hard to tune. But my questions are: is that the only reason? is it always the case? and is it not as much of a problem for viola and cello and bass for some reason?

I would agree that scoring for three violins in unison would sound more pleasant (sounds like a group) rather than two. Also, it's much better to hear two violins in harmony/counterpoint rather than unison to emphasize both violins. Otherwise, you could encounter some trouble with intonation; what I mean is two violins in unison could sound somewhat harsh because of subtle differences in frequency between two violin players so you might as well make them play in harmonies.

It's a bit similar to two overdriven electric guitars playing unison melody lines; there isn't much of a point rather than a weak attempt at thickening up the sound.