The Choirmaster's Manual/Chapter 5
BLENDING THE REGISTERS
In Chapter III the head-tones were attacked and brought down the scale; on this principle all the registers are blended, and the voice made even.
Below are the various ideas held by some leading choirmasters as to the "division-notes" or boundaries of the various registers in the boy's voice:
The registers in a boy's voice are chest, medium (upper and lower), and head. In the first example the word chest is used for medium tones; as before mentioned, the real chest-tone below E
(Lower Medium Resonance felt in highest part of back of mouth, on hard palate. Upper Medium felt on top of mouth, well forward. Head Resonance felt at the highest part of back of head.)
Voices trained on this plan blend much better with women's voices, and don't stand out, but add brilliancy only.
Contraltos (or altos) use "chest" and "medium" registers only. The chest-note resonance is felt in the lower or upper chest, the changeoccurring on Middle C for altos or contraltos only.
The principal break in the voice is between "upper medium" and "head," occurring on D; the break is very seldom noticed between lower and upper medium.
Exercise 9.Take any head-note and train downward over the "break."
When the lower note can be taken with the same resonance as the upper, the scale-passage from lower note upward may be attempted, always singing piano.
Exercise 10.Right up the scale
Start in head-voice, sing very softly. In so doing, the voice will unconsciously get into the medium register, which is what is required.
Wrong head-tone production is combined with a loss of all facial expression, a fixed chin, and a stony eye.