Calling one of the vocal registers the ‘head voice’ is a trifle misleading. Many teachers use the term ‘head’ to describe what they believe to be a type of resonance. The ‘head voice’ is not head resonance. What resonance is to be found in the nasal passages is so negligible as to add almost nothing to the vitality of the tone. The nasal passages are small, non-adjustable cavities and, consequently, highly unsuitable for tonal amplification. They are not important to correct singing.
The ‘head voice’ is another matter. Like any tone, it has characteristics of resonance, or it would not be a tone. However, vibrations which appear to direct themselves into the head are caused by a specific kind of adjustment shared between the crico-thyroid and arytenoid muscles, i.e., registration. Without the right kind of coordinate relationship between these two muscle groups the illusion of the tone being in the ‘head’ would never occur. There is no way of activating the ‘head voice’ by means of resonance, only by registration. To confuse these two is to confuse the training itself. Thinking of the ‘head voice’ as ‘head resonance’ leads away from a clear understanding of the vocal function.
Reid, Cornelius L. The free voice. Coleman-Ross, 1965.