My friend, Daniel Shigo, writes/compiles an extensive, inspirational and helpful blog called VoiceTalk.
I recently read Daniel’s article on “The Focus Vowel,” which relates to methods of my own teacher, Margaret Harshaw. He is quite accurate in his comments about her teaching. We would usually vocalize in the order of [i,u,a] to find both core and focus (most often, with florid vocalises). We find brilliance and power in [i]. We find warmth and roundness in [u], and they combine in [a]. Each needs the other.
In the comments, Daniel makes the excellent point, to “think” about a vowel is the best way to positively impact your tone. As you know from my own writing, it is the imagination that brings about coordination and maintains the freedom to access flexible strength. Don’t “set” your primary articulators (tongue, jaw, lips) into a given vowel position. Rather, allow the thought of vowel to bring about subtle changes throughout the vocal tract. This is one place that support/appoggio and articulation intersect.
Bravo, Daniel, for this excellent post, and for your very interesting site!