Vocal Cord Oscillation

Weekly Teaching Tip – July 31, 2018
by Dr. Curt Stock

I recently finished the first block of Dr Titze’s Summer Vocology Course. It was extremely challenging and up lifting. I love learning and studying the science of voice; for one who doesn’t sing, I now find myself analyzing all types of sound. Dr Titze has taught me much, he is never judgmental and seems to always find something correct in what i say, and then corrects any errors without embarrassing me, hence he makes me want to learn more, the mark of a true teacher.

I want to comment about vocal fold oscillation; most of what i will write about comes from wonderful concepts learned from Chapters 3 and 4 in Principles of Voice Production. This is my understanding of these concepts. Vocal fold oscillation begins with the understanding that vocal folds are sucked together by the negative Bernoulli effect on the glottis. Three things have to take place:

1. The glottis has to be sufficiently narrow.
2. The airflow sufficiently high, and
3. The medial surfaces of the vocal folds are soft enough to yield.

The Bernoulli equation predicts self-sustained oscillation only when there is an alternating convergent-divergent glottal shape. Convergent for opening and divergent for closing.

In other words, the lateral cricoarytenoid muscles and other intrinsic muscles bring the vocal folds close enough together so the airflow can cause oscillation. The airflow has to be adequate to make this happen and the vocal folds have to be soft enough on the contact surfaces to yield to the airflow.

Bernoulli’s effect is the negative supraglottic pressure which causes increased velocity of the airflow and also helps in squaring the vocal folds. To understand this we need to review the science in Bernoulli’s equation.

Pressure + 1/2 density x velocity squared = a constant

So for airflow to remain constant, if we increase pressure we actually decrease velocity or decrease pressure increase velocity. The example of a traffic jam has been given. When we approach the narrowing of a highway from 2 to one lane we are told to slow down. Instead, if we trusted all other drivers we should speed up in an orderly fashion and the traffic would not back up, but would flow without slowing or damming. This is what happens at the glottic level. The application to voice production is obvious. Balance of the voice is key to healthy vocalization.

I would encourage all of you to attend the Summer Vocology Institute next June and July; I took the first 3 weeks and plan on finishing next summer. Teri is planning on the whole 8 weeks at once. Some of the brightest and up and coming minds attend. It rejuvenated me.

Thanks, Curt