As I previously mentioned, the tongue is often a source of unwanted tensions for singers. It is important to be aware of the engagement of the hyoid or digastric muscles at the base of the tongue, near the chin. Just the awareness of their activity helps in loosening their grip. Place both thumbs under your chin and sing an ascending passage. If you feel pressure from the tongue pushing downward, those muscles are getting in the way of efficient tone production. Also, if when watching yourself in a mirror you notice your tongue pulling backward in your mouth, it is being disruptive to good singing. WE DON'T WANT THAT!!!!!
I like to start my warmup time with some tongue stretches before I actually vocalize. This routine I learned from Nate Waller, who was my speech pathologist when I was preparing for vocal fold surgery. Since then, they have become a regular part of my daily regimen.
So here goes:
1) Stick the tongue out of the mouth pointing upward. Hold for 3-4 seconds and release. Repeat 3 times.
2) Stick the tongue out pointing downward for 3-4 seconds then release. Repeat 3 times.
3) Stick the tongue out to the each side of the mouth for 3 repetitions, holding for 4 seconds each time.
4) With the tip of the tongue behind the lower front teeth, extend the body of the tongue forward and out . Hold for 4 seconds. Repeat 4 times.
Make this a regular part of the vocal warmup process. You will be so very glad you did!!
I like to monitor the activilty of the muscles under the chin throughout my practice time. If I feel that my production of sound is getting more difficult, I place the thumbs under the chin to check for tightening of those evil tongue muscles. Often, that is the source of the imbalance. If you're like me and had a lot of problems in this area early on, you must remain vigilant in self-monitoring.