The Singers Formant cluster is mostly regarded among men. It is the clustering of F3, F4, and F5.
SFC occurs when:
(1) there is firm glottal closer (a bright ring in the voice),
(2) a low and stable laryngeal posture,
(3) the aryepiglottic sphincter is narrowed,
(4) and the pharynx is open.
These four things must occur in order to create a convergent resonator which ensure the timbral depth of a low F1. The acoustical space of the throat creates a lower threshold of breath pressure and glottal resistance... which is called inertive reactance. This boosts the singers sound to 2500-3500hz and allows them to be heard over the orchestra. Teaching your student to hear the acoustic event occur in their own singing is important. Teacher and student must take the time to train their ears to hear subtle differences in order to accomplish this acoustic event.
How would you teach this?
use closed vowels such as [u] and [o].
Begin with speech-like gestures on [o] and [u] in speaking range.
Move to a sustenuto exercise in the low register with these closed vowels; make sure the laryngeal posture stays relaxed and stable as you move up in pitch and change vowel variances.
Move to small leaps to larger leaps, all while maintaining a low laryngeal posture.
This takes A LONG TIME to strengthen in a voice, doesn't happen over night... Just thought I should say that... for some reason.... ok. that's all. :-)