Placing or "focusing the voice" I have found to be chiefly a matter of control and use of the resonator, consisting of chest, pharynx, mouth, and the nasal and head cavities.
"Resonance in Singing and Speaking"
Thomas Fillebrown
If to this we connect a long aerial, the length of which has been adjusted to be one quarter of the length of wave corresponding to the frequency, in other words, to make it a quarter-wave resonator, then powerful oscillations will be accumulated in this rod.
"Hertzian Wave Wireless Telegraphy"
John Ambrose Fleming
3. The throat, mouth, and the nasal and head cavities for a resonator.
"Resonance in Singing and Speaking"
Thomas Fillebrown