Consonants articulate words while sustained vowels carry the voice into the world. We do not intone on a [g] or a [t] or a [p], but how forcefully or gracefully we produce consonants affects the vowel that follows and contributes to the quality of the voice.
Each vowel naturally has a different shape and quality. EE can sound clear and outgoing while OOH can sound soft and gentle. AH is in the middle with a combination of brilliance and warmth. Part of developing a consistent tone is in minimizing the differences between vowels.
“EE” as in feet and “A” as in cat make use of resonance in the nose and front of the face. “OOH” as in shoe and “OH” as in note open more into the back of the mouth and throat. By alternating between “EE” and “OOH” we can learn how to keep the brilliance of the “EE” in the “OOH” vowel, and the openness of the “OOH” vowel behind the “EE”. We can then insert “AH” in the middle and try to get all three sounds to be similarly balanced. “EE-OOH-AH-OOH-EE.”
Singing teachers and speaking coaches will often use vowel exercises not only to develop consistency, but also to shift vocal quality. Practicing bright, forward vowels helps with clarity and audibility. Practicing warmer, inside vowels reduces edginess and intensity.
The quality of vowels can also affect mood and energy levels. Bright vowels are more likely to stimulate positive endorphins and boost immune response. Warmer vowels are more likely to support relaxation and receptivity.
Sing or speak different vowels and see if you can feel where they resonate in your face and body. Play with exaggerating differences as well as equalizing sounds. Work these in combination with optimal breath support for the best vocal production and tonal quality.