Some things I suggest that have helped my students loosen tongue tension:
1. Wake up the face and do tongue tanglers, trying for clarity and not allowing the voice to "fall into the gravel" at the ends of phrases. Act like you are speaking to deaf people... make your lyric show in your face. This gets it out of the back of the throat and stiff jaw.
2. Speak or sing with the jaw moving in sort of a slight chewing motion. Tongue tension and jaw stiffness go together.
3. Put your knuckle inbetween your molars (not the front of your mouth) and sing. It will sound weird, like trying to speak with the dentist's hand in your mouth, but your jaw and tongue will experience having to relax.
4. Sing only on the vowels for a while, again allowing the back of the mouth and throat to fall open. This is harder than you think, you have to concentrate on NOT forming consonants. Then allow yourself to slightly let the consonants sneak back in, but keeping the back of the tongue feeling the same and letting the jaw relax flexibly.
5. Put two fingers under your chin. You are feeling the base of your tongue. Speak or sing, telling yourself not to tense there (bunch the muscle up).
6. DO NOT OVER-WORK the tongue in specific vocal exercises. Sometimes I find that exercises designed to stretch out and loosen the tongue can have the opposite effect. If you do these, be sure and note how they actually affect your tongue root's ability to relax.
By the way... some people can do tongue trills and some people can do lip trills and some people can do both. Just like rolling the tongue, forming French or German syllables, for some people it is easy and some hard, because there is a learning curve that makes it easier in childhood, and I believe, subtle muscle coordination differences in people. It doesn't matter if you can do these things or not. The main thing is to get your articulation out of the back of your throat, and there is more than one way to accomplish this goal.
Let me know what works for you!
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