In voiceless sounds, what happens to vocal fold vibration?
In voiceless sounds there is no vocal fold vibration. Unlike in voicing, where the arytenoids bring the folds together to begin a cycle of vibration, the folds are left open during voiceless sounds so that the air from the lungs can pass through freely. Because there is no subglottal pressure increase caused by bringing the folds together, the airstream passing through the open folds in voiceless sounds is not as fast-flowing as it is for voiced sounds, and thus no Bernouilli Effect takes place. Because there is no vocal fold vibration during voiceless sounds, we often say that voiceless sounds give us no sensation of pitch.
