Wim:
Thanks for the post. I don't disagree, but you are not addressing a key element in the changes from "heavy ('rolling' movement with high vertical phase difference and high closed quotient) or light (lateral movement with little vertical phase difference and lower closed quotient). The vocal folds are made up of 4 (some say 5) layers. From median laterally they are: mucosal membrane, vocal ligament and two thyroarytenoid muscles ( I do not have my reference materials here so I must generalize). The "little vertical phase difference" description you mention is the result of the vocal ligaments being the primary resistance elements to the lengthening of the crycothyroids. The "rolling movement with high vertical phase difference" of which you speak is the result of the active involvement of the two thyroarytenoid muscles.
Open and closed quotient has a very strong effect on the tonal quality but this is usually described as "pressed" phonation (vocal folds closed during most of the oscillation cycle) or breathy phonation (vocal folds open during most of the oscillation cycle) aor the desirable correct phonation (a more or less equal balance between closed and open of the folds during the oscillation cycle). It is possible to use any of these quotients in either light or heavy mechanism. Tthe light or heavy is more a description of the thickness of the vocal folds and the portion of the vocal folds that is oscillation than it is a description of the closed or open quotient.
Also the is no function of which I am aware in which there is "completely dominant vocalis (or) completely dominant cricothyroid. Depending any use, one or the other of these muscle will be dominant but not without some antagonistic action of the other.
You also state: "Also it seems that the point at which the mode transition will occur is not exclusively determined by the ratio between the activity of the two muscles. Other factors such as adduction force / subglottal pressure as well as resonance can influence the point of transition."
I agree. Especially the effect of resonance on the points of passaggio change. The vowel chosen can change the passaggio point as much as a major third to a fourth because of the effect the standing wave has vocal folds, that is, the acousitic load that applies to the vocal fold.
Titze, in his book, stresses the idea of vocal ligament and vocalis muscle and the affect of acoustic load on the vocal folds -- Lloyd W. Hanson, DMA Professor of Voice and Vocal Pedagogy, Emeritus Director of Opera-Theatre, 1987-1997 School of Performing Arts Northern Arizona University Flagstaff, AZ
|