This is when the the vocal folds close, open and close again so that they return to the same position at the beginning of the cycle (Link). The vocal folds form a narrowing of the air passage (a). When the air stream passes through this narrowing, a partial vacuum is created, thus bringing together the mucous membranes of the vocal folds. (The same effect occurs when a bus passes you at great speed, you can get sucked in behind it and is known as the ‘Bernoulli effect’). The movement where the membranes close is called the ‘closed phase’ (f-j). The closed phase begins with a suction movement at the bottom edge of the vocal folds and moves upwards in a rolling motion. In the closed phase the flow of exhaled air is momentarily stopped which creates an increase in pressure beneath the vocal folds (‘compression’) and a relative decrease in pressure above the vocal folds (‘rarefaction’). The upwards rolling motion ends with the vocal folds separating when the pressure is released (k). Now the folds have completed one pulsation/vibration or vibratory cycle and are ready for the next one. This repeated interruption of the air stream by the mucous membranes coming together creates a series of pulsations known as a ‘sound wave’.
Vibratory cycle RS_admin