Once in a while, I will see a tenor in mid-career, who comes to me with a high note crisis. This kind of singer has enjoyed considerable success with a dangerous technique; he has learned to sing the high notes with a stentorian sound and tremendous compression. His method is to depress the larynx as he approaches the top, and to support like crazy.
Most of us, I think, are in agreement that to sing well, the larynx has to be comfortably low. “Releasing” or “loosening” the throat is a cornerstone of technique for many teachers. Pressing on the larynx can be an addictive approach for several reasons.
1. It really feels like “doing” something. Unlike more imaginative approaches, it gives you something that you can physically do as you approach the upper register.
2. It may work really well for a while. The memory of this success will keep you at it long after the approach ceases to function effectively.
3. It has an appealing simplicity. "Push down, sing high".
Eventually, the cords no longer want to approximate with the voice box under all that pressure. The medial compression which serves to keep the cords together no longer seems to function. At this point the singer is cracking virtually everything over an A flat in performance.
The solution is to substitute an imaginative approach for a physical one. That means the singer has to have great trust in the teacher. Doing it right always feels like much less than forcing did; and it is hard to believe that an imaginative picture of the loose throat and the progressively higher palate will help at all.
There is a famous story from one of the meditative traditions (I forget which one) of the monk who had a profound experience of illumination, and then spent the rest of his life trying to recapture the experience, to no avail.
Experiences cannot be recaptured. When an approach fails you, even if it worked in the past, let go of of it. Have the courage to approach things in a different way.
In singing, we keep going back to basic principles; good breathing, good support, a feeling of forward clarity and lightness in the voice, a loose throat, a healthy onset and an imaginative picture of the vocal space, that allows room for development as you go higher. Rounding or vowel modification can be a helpful way to make the transition to the upper register, provided you don’t get stuck.
In my experience, interfering with the larynx always leads to trouble. The quick fix will get you there sooner; but it will lead to collapse over the long haul.