The vocal cord is composed of muscle and folds of mucosa, and does not move by itself without contracting these muscles.
The vocal cord closes to narrow the path of breath. The vocal cords then vibrate by exhalation and make sound.
The closing and opening of the vocal cord are done by muscles, which attach to the arytenoid cartilage, such as the posterior cricoarytenoid muscle or the lateral cricoarytenoid muscle. All muscles moves by themselves.
However, there is another way to close the vocal cord.
When the expiration of air is passing through the glottis, the muscles becomes the negative pressure around the glottis and the vocal cord gets closer to each other. We call that “Bernoulli’s theorem”.
If you exhale more, it is easier to let out a strong voice, because you can open and close the vocal cord naturally without using a lot of power.
There are two important points that have to be in consideration to use Bernoulli’s theorem.
(1)Be aware that, more expiratory pressure will make the vocal cords closer.
(2)The vocal cords will not get closer if the vocal cords’ mucosa is not present and flexible.
If either one of the above stated factors are missing, then applying the theory to the will be unsuccessful. Practicing and exploring different training and breathing techniques is truly important when figuring out which route is the best and most efficient in improving your voice.