You can’t really talk about squillo without talking also about the “path of the breath” – “il giro della voce” – the curved path of the voice as we ascend in the scale. So point #8 from my original list of things:
The combination of squillo and first formant in the middle voice; more squillo and turn to 2nd formant from F# to G# (drinking the sound); and from A Natural up, a dominant sensation of squillo with less affondo (depends on strategy), a sense that the voice has its vibratory pressure less in the throat and more into the mask.
The ability to combine masterfully first and second formant sound with squillo is an important quest in male opera technique. First thing you need is of course, the sound. The cords have to produce harmonics efficiently and abundantly. Tuning the harmonics is an outgrowth of that.
I do not like bland food without salt. However, no one would eat a block of salt. Similarly, if your mental intention is to exaggerate the functions that yield higher harmonics at the expense of lower ones, you end up with an unpleasant voice. Squillo is correctly found when a balance between lower and higher harmonics is found.
Finding this balance means knowing how your voice changes throughout the range. So here is your blueprint.
From lowest notes to about an A3, the tenor voice is very focused. The sound seems to move like a beam from larynx to the frontal sinuses. Depending on how chesty your voice is, the stronger the laryngeal lean is.
In the range between A and F the voice takes on significant first formant strength. This means that the singer feels the voice expand vertically toward the soft palate area. If this is done correctly, the squillo remains strong. Otherwise, the voice goes backward. Italians would say that the voice “risuona indietro” – or is back.
As you go above the F, the voice “turns,” meaning that the sensations move more into the mask. This occurs because we start tracking the 2nd formant. Squillo picks up in intensity, and the sensation expands above the palate; hence, the old masters spoke of the voice having a path, a curve into the mask.
One last word about this path, as we can see in both Gigli and Lauri Volpi, Cotogni’s method focused on “Eco Sonora” or 2nd formant dominance from F to A-flat. From A-natural upwards the focus was more toward the 5th harmonic.
So what this equates to sensorially is a feeling of the voice filling the mask from front to back in the F-Ab range, and then moving really forward into the area right behind the eyes from A natural upward. In order to truly develop an old school sound, the tenor must maintain the 1st layer in the sound. It acts as a cushion against excessive pressing.
I am attaching an audio clip with a few examples of this path.