What is unpressured phonation, and how does one perform head resonance?
Unpressured phonation is talking about the way the vocal cords come together and vibrate. A pressured phonation would sound like a little grunt at the beginning of the sound as a result of the cords being forced together before the flow of air begins. This is called a glottal stop. Occasionally a mild glottal stop is used to begin a vowel, but over time an exaggerated stop can cause fatigue and even damage the cords. It is more desirable to have the cords come together gently as the flow of air begins with no audible glottal stop.
Head resonance is accessed by shaping the articulators so that the sound reverberates in the openings in the head — the mouth, the nose, and the spaces behind them. The most noticeable changes will be in the shape of the tongue, the soft palette, the lips and the jaw although many other articulators are involved.
Richard Miller’s THE STRUCTURE OF SINGING is an excellent resource for vocal function and techniques.