The correct tenor production in the passaggio is tricky, and is also diverse. There are many ways to approach the passaggio considered successful, and frankly aesthetics have evolved over the last century.
Cotogni’s Italian patrimony passed on to his famous students (the eco sonora – a strong 2nd formant strategy in the passaggio) has become thoroughly part of the operatic consciousness thanks to Pavarotti, Corelli, Tucker, and others. But there are other traditions also once very widespread, like the Caruso/Bjoerling approach, which I believe is a more pan-European approach (particularly French and Northern influence), which didn’t emphasize as much the cupo sound (which migrates the vowel more toward an OH) but brought together many other vowel components.
For example, Delle Sedie quite clearly sets forth how he would approach the passaggio by bringing vowels closer to French nasals. Northern Europeans used their umlaut sounds to aid them in this process. I think the Italians favored the eco sonora (2nd formant tuning) so much because Italian doesn’t have nasal or umlaut sounds.
An example of Italians with a more European approach to the passaggio is in fact, Caruso. Listen to how he approaches the passaggio work in this recording of E Lucevan
One thing both traditions (Italian Eco Sonora and European mixing of vowel components) has in common is the idea that in the passaggio area of the tenor as the voice turn from Chest to Head, the voice will strike the mask forward in the forward maxillary sinuses – le fossa paranasali.
This is an interesting phenomenon very much linked in my opinion to the importance of keeping control of the epiglottis and avoiding its excessive lowering.
We are taught in the Italian school that we should “drink the sound” – very much linked to the phenomenon of appoggio. Often, singers in doing this, or in seeking cavita’, the spacious sound below the soft palate, engage in lowering the epiglottis excessively without even knowing it. I have trained my ear to hear it, but many don’t know what to listen for. The tongue staying forward in the throat and the epiglottis staying up opens the vowel differently in the middle voice. Listen to Zenatello demonstrating how the vowel opens up without pressurizing – he simply tunes it differently because the space in the throat will allow it.
When the epiglottis stays out of the way and the vocal folds are closed well, the sound just flows into the mask as you ascend into the passaggio. You can think of the voice as having a sort of sound pressure… like a cloud of resonance that seems to find a path of least resistance. When the “impostazione” – the vocal set up – is correct, the voice gets wider and darker right below the passaggio and then forward in the mask as we turn into head voice. The sensation of the sound pressure gets closer to the nose as we get closer to the passaggio, even though the sound gets wider and darker. The instinctual tendency would be to think of expanding the sound in the throat like in a yawn. The physical opening of the throat, and the sound pressure should be thought of as two distinct things – separate workings.
Lauri Volpi tells us how as we approach the passaggio and into it, the soft palate has a slight sense of lowering, and the curve of the breath bends forward, lest the voice fall into the cavernous pharynx. I find this extremely enlightening as to his method. The open pharynx and the voice striking forward in the nasal area are TWO SEPARATE THINGS. Just because the tongue is forward in the throat and the epiglottis up (creating more pharyngeal space) doesn’t mean that we should let the sound pressure stay there! Lauri Volpi also gives us another clue by telling us that those who do let the voice sink into the pharynx show that they do not understand how to measure the breath and don’t know how to insert “tubo risonatore e tubo pneumatico” – sound tube and air tube… the juncture of sound and air pressure at the larynx. We should NEVER push more breath at the passaggio. We should instead TUNE the sound so that the voice can expand where it should. The sound like a living vibrating mass expands or has a sound pressure that is linked to the way the actual breath pressure and larynx work together. As we ascend from middle to passaggio above we should think that the sound pressure is expanding in a different place, but this doesn’t require us to push more breath pressure. To do so ruins the “canto di posizione” – or our ability to sing from a position of flow, grounded in the body. If you start throwing air at the to voice where will you stop? You get into a hall and you want to push more. You shouldn’t change the breath pressure ( or at least you don’t feel like you do in the larynx, even though the actual breath pressure does increase which is why we have a slight upward movement of the chest). You sing from a position and you tune the sound by making the correct adjustments. You shouldn’t confuse what I just said with the use of aspirates, like an H sound in front of a high note. That is a trick often done to relieve excessive pressure beneath the chords and to kick start the high note. I think it is a bad cruch, but it works for many. The “throwing air” I am talking about is the sense of needing to push more air pressure into the voice because we are going up – the very thing the aspirates want to relieve.
The invitation to drink the sound can be tricky because you may think of drinking and lower your epiglottis like you do when you swallow, which would in fact increase your awareness of the sound that expands in the pharynx, and you may think “Ah this is appoggio because my sound is down by the larynx.” This is not appoggio. The idea of “drinking the sound” is very subtle and is more about the sound feeling like it originated laryngeally EVEN THOUGH THE SOUND PRESSURE MAY BE SOMEWHERE ELSE. This is hard to explain…
Think of your voice as having both an origin and a resonant pressure… When you sing with deep breath, your larynx relaxes in a low range and it seems that the voice that is going up into the mask in the upper range originated from a low laryngeal place. If the sound lifts, or loses its connection to this lower origination point, the sound gets smaller (because the lower harmonics weren’t balanced). Once the breath support is correct and the larynx relaxed in a low range, this becomes more intuitive. But remember what I am saying, just because the larynx is low and the origination of the voice is low doesn’t mean that the sound pressure stays in the throat. Like Lauri Volpi said, it moves into the maxillary sinuses as we learn this sensation of soft palate lowering with open pharyngeal space and do all this with closed chords. THESE ARE ALL DISTINCT OPERATIONS and that is why it takes so much time to train. You have to do exercises that teach you to deal with these workings individually and holistically.