Duet dissonance: the experts speak

I posted a question in several newsgroups about duet dissonance, especially as it applies to four violins. I received replies from several top-notch experts--a physicist and several sound reinforcement and recording professionals. (If you're not familiar with Usenet, you can find my question and the answers by searching Google Groups for "Gotchas with four violins".) Here are some of the results:

What causes duet dissonance? It's due more to vibrato and slightly-out-of-tune notes, than to clashing harmonics, though all are a factor.

Do sound pros recognize this problem? Many of them do, though a few haven't heard of the issue.

There's a pattern: those who closely mic the violins seem to perceive a bigger problem than those who work with small ensembles in live performance settings. I attribute this to the tendency of room acoustics to blend the sound.

For what number of violins is this a problem? Everyone agreed that duet dissonance is really a problem only in the case of two violins. Adding more instruments masks any ugliness. Four violins (2 unison pairs) don't pose a serious problem.

What about the use of unison pairs of violins in classical music? While not common, there are plenty of pieces where composers call for two violins to play in unison. I think this works due to a few factors: the blending effect of room acoustics, playing style, and subjective factors (is it "sparkle" or is it "dissonance"?).

There were also some great comments on tangential topics, such as how to mic orchestras or what kind of mics to use. I'll address these in some future articles.