I've recently been doing quite a bit of American accent coaching, and it has come to my attention that we as actors are vastly unprepared when it comes to the simple question: what's going on in my mouth?
"Bah humbug!" You say. "Actors don't need to know about the aryepiglottic folds! It's all about being in the moment!" To which I say, fair enough. I don't want you to start thinking about your oral twang mid-scene. But as it is better to be informed rather than ignorant, I would argue that it's better to be so versed in the workings of your own mouth that you don't need to think about it, as opposed to realizing mid-scene that you have no idea what you are doing.
But what is this even good for you ask? For one: accents. In an accent you will be changing, sometimes ever so slightly, what your tongue, jaw, lips, soft palate, etc. are doing. Knowing your way around your mouth is also needed for character voicing, when creating a voice for a character that is distinct but also consistent. I would argue you can only do this continually by knowing what is happening in your mouth.
To start: a bit of science: vowel sounds are all created in the same way, as the vocal folds in your larynx vibrate creating sound waves. The vibration then passes through your oral cavity (known at the mouth and throat in normal-person speak) which changes shape based on the sound. It is through the position of the tongue, lips, soft palate, and jaw that changes the vowel sound.
1. To start, spread your lips into a smile, and push your tongue high and forward. Now see what sound comes out when you out some voice through it. Chances are you will get an 'eee' sound. This is the most forward and high vowel sound we can make.
2. Keeping your tongue forward, move it down a fraction of an inch, and you arrive at 'ey'. I think of this as the Italian exclamation "AY!"
3. Keeping moving the tongue down but staying forward and you land on a nice, solid 'eh' sound. This sounds vaguely English, such as in the word DRESS.
4. Now going as far down as you can with the tongue at the front of the mouth, you will find yourself square on the sound 'aeh' as in the word TRAP.
5. Let's start to move the tongue back in the mouth, but keeping it low. A few centimeters back from the previous sound you will find yourself producing a short 'ah'. This sound comes in handy when doing Northern English (UK) accents, such as in the word BATH.
6. Going as far back and down as you can with the tongue, you'll find yourself in new territory, producing the sound 'ahhh'. This is the sound found in the standard British BATH. For Americans, this sound is found in the word FATHER.
7. Now let's move the tongue up again, but keeping it in the back of the mouth. Round your lips over this sound, and out pops a nice round 'awww' or 'or' sound.
Note: Americans! This sound occurs a lot in UK accents, popping up in words such SHAW, LAW, NORTH & FORCE. In General American speech it shows its face in 'or' sounds, if you pretend there is no 'r' pronounced.
8. Moving the tongue up, you'll pass quickly over a very pure 'ooh' sound. You know the one.
9. Finally, bringing the tongue to the top we reach our highest back vowel 'ew', as in 'u'.
Now relax everything and reward yourself with the most lazy sound you can make: 'uh'. Voila, you've found your schwa, or most neutral vowel.
There are a few more vowels that fall in the middle, but you now know where the vowel homes are in your mouth. Now that you've paid them a visit, the quicker they will open their door to you in the future.
Happy vowel exploring!