Dear Mary Beth and Vocalisters:
It is my understanding that the sustained oscillation of only the mucosal
membrane occurs when the vocalis muscle is in a more relaxed state and the
longitudinal tension on the vocal folds is sustained primarily by the vocal
ligaments. The pitch that is produced when the vocal folds are in this
mode of operation is high, that is, near or at the top of the female or
male range.
In the middle or lower ranges of the voice it is typical for the vocalis
muscle to supply some of the longitudinal tension on the vocal fold because
the vocal ligament is not stretched at or near its maximum tension and is,
therefore, not a contributor to the necessary longitudinal tension for the
pitch being sung. In this vocal fold mode of oscillation, a larger portion
of the vocal fold is in oscillation, including part or most of the vocalis
muscle.
I am not sure without checking my resources what configuration of the vocal
mechanism creates the medial tension that is often mentioned on this list.
Medial tension would, by definition, be a pressing together of the vocal
folds at their midline longitudinally. It would not appear to me that a
complete closure of the thyroarytenoids would accomplish this by itself.
Also, a closure of the space between the thyroarytenoids, which is common
in full volume singing, by activating the interarytenoid muscle has a
tendency to slightly open the extended portions of the thyroarytenoids
which would open the vocal folds at their posterior portion. Such an
opening is commonly closed by the vocal folds themselves but I am not sure
what muscle action accomplishes this. It could be that this vocal fold
muscle activated closure is also the cause of the medial tension but that
is just a pure guess.
I know this is a lot of big word stuff but I don't how else to discuss this.
Regards
--
Lloyd W. Hanson, DMA
Professor of Voice, Vocal Pedagogy
School of Performing Arts
Northern Arizona University
Flagstaff, AZ 86011
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