How Is Sound Produced

 

To make sound for speech, the vocal folds are first brought together by the muscles of the larynx. While they are closed, the action of the respiratory muscles and the chest wall cause the air pressure below the vocal folds to increase, then eventually the pressure beneath the vocal folds will exceed the pressure holding them together, and a burst of air will escape through the folds. As air flows rapidly through the larynx, it will create a decreased pressure which we call the Venturi effect, and then the vocal folds will be brought together.

The pressure beneath the folds will rise again and the process becomes a cycle. This process of rapid opening and closing produces vocal fold vibration. Each time the vocal folds open, they produce a jet of air which creates rapid changes in air pressure that produces the sounds we use to make speech.

Generally, the vocal folds do not produce sound by vibrating. The sound is actually produced by the pressure changes created as small jets of air pass through the moving vocal folds.

 

The sound produced by the vocal folds consists of a series of harmonics. The lowest harmonic, also usually the strongest, is called the fundamental frequency. For men, the fundamental frequency is about 100 Hz, slightly higher in women and children.