Anyone who wants to make a beautiful sound must tighten the vocal cords, otherwise bad habits will easily lead to poor closure. This process is a "gradual tightening" process, that is to say, the vocal cords become shorter and thinner, and this process is also gradually changing voice. What we usually call the closing of treble is the concrete embodiment of this process. For example, in the practice of U sound in Bel Canto, it is not fundamental to simply deform vowels and add "U" or other vowel deformation methods. Some people have no ability to "concentrate and tighten" their vocal cords at all. Even if you distort their vowels, they can't sing high notes.
Turn left | turn right
Some people's vocal cords are born with this ability, so they can easily solve high notes. This "gradual tightening" of self-feeling is a kind of "suffocation". Pavarotti described this feeling. This feeling is called "tightness" and it is easy to sing high notes. "Core" is the final result of the tension and concentration of vocal cords.
At this stage, the problem of vocal cord closure is solved! ! ! !