First off, a simple explanation of the word resonance is, sound building with echos. Sound bounces around and combines with its echos to change and grow. That’s the simple version.
Now that we have established that, let me get controversial.
There is no such thing as a “Chest Voice”. There is no vocal resonance of any value occurring in the chest. Just like there is no “Head Voice”. If you have a brain rattling around up there, there is no room for sound to do the same.
All the sound comes from the vocal folds in the larynx in the throat which is the first area of resonance. That’s why I call it the Throat Voice. It then resonates in the mouth or Mouth Voice (commonly know as the Modal Voice), then into the nasal cavities or Nose Voice.
And really those three are separations of resonance in order to simplify explanations. You only have one set of vocal folds, ergo one voice.
What many are calling the “Chest Voice” is actually full resonance. I sometimes have my students concentrate creating it in the Throat Voice but physically speaking it is ALL voices opened up as much as possible to allow the most resonance as possible.
All singing, especially high notes, require air flow and space to resonate without backing up.
Simple proof of this is the humming test. Hum and then pinch your nose closed.
Everything stops. There is no way to hum with your nose closed.
If the air is being backed up to the vocal folds (cords) due to constriction of resonance, the vocal cords are burdened with additional task of pushing through sound that is bouncing back at them. Thus strained, they can’t reach their full potential of range.
This applies to extreme low notes as well. Try slouching, tilting your head down and singing your lowest note. Now try straightening up, look straight ahead, tilt you chin down slightly and sing your lowest note.
Which was easier and lower?
Failure to Launch
With the high notes we need all the room we can get to allow the resonance to grow up and get out.
That means extending the neck by dropping the shoulders back, bringing the tongue back and down, opening the mouth and nose as much as possible for the resonance to be expelled as vocalization.
The problem with EEE’s and OOOO’s is that that Vowel Shapes themselves are constricting and counter-productive for full vocal resonance.
Unfortunately, without changing vowels, nothing can be done about it. But wait…
What if we cheat a little?
Drop the tongue a little with the EEE’s and make them slightly more ‘Eh’ as in the word ‘it’. That gives you a little more room for the sound to flow.
With the OOOO’s drop the jaw ever so slightly and move the tongue back slightly as well going from the OOO sound to more of a closed ‘Oh’ sound as in the word ‘goat’.
This gives you a little more room, but still not as powerful as words with ‘I’, ‘A’, and ‘Ah’.
That’s why you don’t hear a lot of songs with really high notes using constrictive vowel shapes.
Try that and let me know how it goes.