Mike,
1. Scott Walker.
In the example you sent, Scott Walker sings in mezza voce or 'voix mixte' as it is some times called. Obviously there is not much of a Singer's Formant to be heard in this kind of production, but that is due to the very light adduction of the folds, whereby they produce much less higher harmonics. This does not mean the SF is not there. It's just not 'filled' with harmonics from the voice source (the folds). Like you said it's possible that the position of the epiglottis influences the SF. In mezza voce the epiglottis is more open than in 'normal' singing, so it could be that the SF is less pronounced.
By the way, maybe you already know this, but one can directly measure the formants with Gram or VoceVista by using 'vocal fry' or 'ingressive voice', so you could try for yourself to see what happens.
2. The 1 to 6 ratio between the tube diameters stems from Sundberg. This seems to be the key factor in SF.
3. Low larynx and power. I'm not sure whether it is possible to produce a significant SF with a high larynx. I will look into this but it seems unlikely to me, as I can't imagine a C&W singer using 'twang' cut through an orchestra without amplification. This brings me to a second advantage of the low larynx. If the larynx is relatively low, the strap musculature of the larynx is more likely to stay relaxed, even in situations where the subglottal perssure is very high (as in loud oparatic singing). Research has also shown that with a low larynx the movement of the thyroid cartilage w.r.t. the cricoid cartilage has a larger 'range', which increases vocal range, but I can't remember the details from the top of my head.
Wim
|