Steve and Vocalsiters:
You are making remarkable headway with Coffin's vowel chart. In fact, your reference to the various register names he gave each of the diagonals on the chart are only now finding confirmation in the writings of many other voice scientists. Coffin's own research and his excellent ears gave him information that was not common during his lifetime and is not very common today.
Coffin's head mix (flute) register is, as I understand it and remember it, a mixture, as you say, of the vowel pitch register and its octave. (I am presently at our lake home and do not have all of my resources with me here.) It helps if one keeps in mind that the various diagonals were placed on the chart from Coffin's experience in the studio, that is, from a concerted effort over a period of many years to discover what vowels worked best in each voice and each voice range. He then sought scientific evidence to either support what his ears taught him or disprove what he was hearing. As he did so it became obvious that a series of vowels tended to emphasize certain of the partials found in the phonated sound. He organized these vowel according to their place within a given partial emphasis and the "diagonals" on the vowel chart are the result. The nice part about the chart is that it can be used successfully without ever knowing or understanding the significance of diagonal names which designate the phonated partial that is emphasized.
So the vowel chart is a compendium of that which was practical in the studio with the support of that which acoustical science could confirm. He did not solve all problems to his satisfaction, far from it. And I have often thought that he was not as sure as he would like about the the composite of the head mix (flute) in the female voice. He did find evidence that formants 3 through 5 moved more closely together in the upper register of the female voice and became, possibly, the equivalent of the "singer's formant" This is not necessarily the same as tuning the fundamental in this register but, rather, tuning the octave above the fundamental or first partial and the fact of its combining with the compressed formants 3 through 5 give the voice great intensity and more than a little confusion for the measuring instruments of Coffin's time as well as the researcher.
Mathematically, the .67 registers does relate to one of the phonated partials but I would have to look it up. It is no longer in my memory.
Does any of this help? Are you using Coffin's Vowel Mirror to assist you with finding the more exact maximum resonating vowel space? Let me know.
-- Lloyd W. Hanson
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