Vowels and combinations of vowels (diphthongs) are usually categorized in two basic categories:
vibration of sound created by placement of tongue - forward, central or back
position of jaw - closed, mid and open
(a third sub-category is also lip shaping)
Most vowels lend themselves to a certain placement, but the most common English vowels are:
A (as in day) = diphthong (moves positions from central mid to forward closed)
A ( as in bad) - forward open
Ah (as in father) - back open
E (as in see) - forward closed
Eh (as in fed) - forward mid
I (as in fight) =diphthong (moves positions from back open to back closed)
Ih (as in sit) - forward closed
O (as in fought) - back open
Oh (as in pole) - back mid
Ooo (as in too) - back closed
U (as in cute) - back closed
Uh (as in puddle) - central mid
Practicing placement can help to get a more specific idea of where sounds are being created in your mouth as well as which sounds are the best for your overall quality. It helps to look at the piece of music you are singing to pick up on which sounds will be "nice quality" sounds and which ones you might have to spend a little more time on.
Back open vowels give nice, round sounds. Closed sounds can be more directed, while closed forward sounds feel more pointed - like an arrow with a specific bull's eye. Central mid sounds tend to be the most difficult to hold on to and keep a good quality.
HELPFUL HINT: Make sure you SOUND OUT your vowel completely, because the written vowel might make you think it has one sound, but sung actually has another. Diphthongs are infamous for this - a combination of vowel sounds.
For example: the word "night" does not only have an "i." When singing this long note, you can take advantage o the "ah" and add the"ee" sound at the very end of the note. This will create a much nicer, more open, thick and powerful sound.
