Many singers "swallow" their sound without realizing it. This happens when you pull your tongue back into your throat, muffling the tone and creating tension. The Th Buzz physically prevents this habit.
The Sound
Tongue tip gently between your front teeth. Make a buzzy "Th" sound (the one in "This" or "That", not the soft one in "Think"). Should sound like a buzzing bee.
The Feel
Strong vibration on your tongue and lips. If the buzz stops or moves back into your throat, your tongue has pulled back. Keep it forward.
The Drill
Sing 1-2-3-4-5 using this buzzy "Th" sound. Focus on maintaining a steady buzz as you ascend. Sustain the top note.
Why This Works
Your tongue is a massive muscle attached to your larynx. When the root of the tongue tenses or retracts, it pushes down on your epiglottis and stifles your vocal folds. Placing your tongue tip between your teeth stretches it forward and prevents it from bunching up in the back. This "un-swallows" your sound and teaches you what free, forward resonance feels like.