I always suspected as much:

http://www.andante.com/article/article.cfm?id=22924

What's troubling me is what you asked google in order to find this!

Actually, I have never understood any sung words, except from ABBA and Julie Andrews! Oh, and Frank Sinatra's generation.

I actually heard this on NPR the other day. Whenever I listen to opera, which is typcially in Italian (of which I know a little) and German (of which I know more), it seems I can never understand anything. I feel vindicated.

Back in my single days I had a penchant for ballet dancers--tall, skinny and dumb. I later learned the charms of opera singers--all that and with preternaturally large breasts.

Pendulantly large breasts!?

Whatever, they all seem to be freaks of nature. (Not that ever minded!)

No wonder my grandfather ran off with one* (ending his marriage). He liked her voice too, I've heard.

Ariel

*Or should I say, one too many? A thing he had.

Sorry to bring this back on topic , but a voice teacher of mine once propounded a similar theory about the unintelligibility of sopranos. Seems that the production of vowel sounds is somewhat dependent upon the proper resonant frequencies in the proper ratios. His reasoning was that as it became necessary to sing higher and higher frequencies (nobody goes higher than a soprano), the positioning and tension on the vocal cords to produce the best overall tone becomes such that the production of the proper frequencies for vowel sounds becomes more and more difficult, and at the top of the register nearly impossible. The higher the note, the more likely it is to come out as just a generic schwa or ahhh-type of sound.

It isn't actually impossible to generate vowel sounds at higher pitches, it's just that the overtones needed to make the vowel intelligible usually produce a more pinched, unpleasant tone.

None of this applies to diction, however. There is generally no excuse for lack of production of unvoiced consonants. Some sopranos (Callas comes to mind) have such gloriously rich tone that you can almost forgive them. Others, like Beverly Sills, manage to nail the consonants without losing the line or the breath. That takes work, work, work, and a substantial amount of concentration and talent.

Yap. I agree with Matt. I'm a mezzo soprano and I sing operas occassionally too. Singing is never difficult, but to make people understand what you are singing without affecting your tonal quality is really, really difficult. Only a few professional opera singers can do that with ease. So don't blame the singers for their bad diction. It's not easy to produce clear souding vowels and at the same time maintain projection and articulating the consanonts.