Okay now that our breathing is perfect, we’re ready to talk about the jaw.
This is a simple principle: your jaw should always open naturally down and back.
One habit so many of us develop in singing is protruding the jaw forward.
This is for a couple of reasons in my opinion.
1. The voice is coming out of our mouth which is on the front of our head, so our brain logically wants to put effort in a forward direction to help the voice out. This is why a lot of novice singers jut the whole head forward, reach up for hight notes, etc.
2. Jutting the jaw forward moves the mandible closer to the eardrum, and we hear more bone conductivity from that internally. It creates an ear-lusion that we’re singing with more resonance.
A couple of ways to think about it:
1. Imagine falling asleep on a plane or bus and you’re doing the attractive open-mouth snooze. That’s the feeling.
2. For more metallic vocal modes, you’ll execute more of a wide lizard overbite look.
If we protrude the jaw (and/or tighten the lips), it causes uncontrolled constriction in the vocal tract, and that makes singing harder.
Another way to practice this: Do what the picture shows when you practice. The loose jaw is for a neutral vocal mode while the bite happens in edgier and more metallic singing. (Image is from Complete Vocal Technique’s literature).