The cords should be longer in the high register, which means 2 things: (A)you will need to know how to keep the cords closed without pressing when they are thin, and (B) the feeling of the vibrant body of the voice will be felt in different ways throughout your range [(a)chest, larynx and mask in low voice; (b) less chest, expanded pharynx, and some mask in the middle voice – between C and F; and (c) far less chest, some pharynx expansion and a lot of mask to increasing degrees as we ascend.]
This is difficult thing to explain, easier to demonstrate. Is there a way for us to know that we are elongating the vocal folds? Sure, just sing like a soprano on your high C. The vocal folds get long and there is very little vocalis effort in the vocal folds, or chest voice; so the resulting sound is “head voice” – the soprano voice.
In order for a tenor to develop ease and harmonic squillo, the cords need to get longer for the higher register. The problem is that when you sing with longer cords, these will tend to not hold air pressure as readily as when you were in chest voice. So, initially your sound will tend to crack and wiggle a lot when you seek a balance.
One needs to find enough chest voice to have sufficient tension on the cord. This is the problem with top-down approaches and falsetto-based methods. If a tenor has a pretty heavy voice, he will tend to lighten up significantly above the passaggio, and the voice may start to wiggle and crack if the balance with chest voice is not established, going back and forth from head tone in a sort of yodel. If the tenor is pretty light he will tend to squeeze a lot in the passaggio area because the chest voice is not aiding sufficiently in closing the cords, and so either greater pressing of the cords is used as a remedy, or lifting of the larynx to close the cords reflexively, or he may just revert to a breathy head tone.
So, the remedies I prescribe are two: (1) exercising appoggio by getting very laryngeal between low and middle C (getting more chest into the vocal function); and (2) exercising voce finta, exercising the muscles that close the cords while singing in falsetto above an Aflat in the passaggio (this means that cords are closed almost exclusively through the effort of the inter-arytenoid). Voce finta is a type of falsetto that resembles full voice. If you listen to it in recordings you may even be fooled. Here is an example. voce finta La Speranza
The high C may sound like real voice because of the more complex sound compared to a mere falsetto. The presence of harmonic squillo is very much present. However, the contribution to this sound of “chest sound” is far less compared to full voice. This is a good way to exercise the muscles that close the vocal folds in the higher register without straining the voice because of the lack of chest. This also is a good way to start mapping out the sensations of vibration linked to the squillo striking the mask. The tricky part of voce finta is learning to not raise your larynx while doing it. The larynx should remain flexible in a low range, not fixed, but relaxed low through the active involvement of the diaphragm. Now remember, you don’t need the diaphragm to produce pressure because this is a light production, but it is important to keep the diaphragm active so that your larynx can relax low.
So, voce appoggiata in laringe (a feeling of the sound being contained in the larynx) in the low range exercises the chest function; and voce finta exercises exercise cord closure without chest. Now remember, the voice is built from the middle. The middle voice is a wonderful range where the voice combines so many different functions. It is essential to have strong muscles in the larynx and cords so as to be able to produce the correct phonation without ever pushing. If the muscles do not respond, we will tend to push to get them to do what we want. We must resist that temptation and keep our baseline phonation: the mental intention of the 1st layer. We have to keep the intention in our mind to never push beyond what we do in the first layer. That is our baseline. The increase in breath pressure, adduction, vibration, etc., is an intensifying of all the relative muscular activities, but not an increase in the driving of the voice. In our mind we should still think of a little gentle foghorn straight tone – that first layer sound beyond which we do not drive. We will feel tempted to drive more in order to get louder, but we can get louder without driving. The voice functions will be intense, yes, and so will the breath pressure, but that doesn’t equate to driving the voice.