Hi all -
I was reading a book my dad got from a charity shop recently. Oxford companion to music - quite an old book. In the section on voice it mentioned that each vowel is actually made up of two pitches (made by two resonant chambers in the mouth. Apparantly the vowel production has to take advantage of overtones in the note - and is only possible of the correct pitches are there in the overtones. That is supposed to be why each vowel is easier to sing on some notes than on others. Higher registers are supposed to be particularly difficult for some of the vowels.
I have explained it very badly - but just wondered whether anyone had any more information or comment on this?

Kris