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How do the vocal cords create voiced sounds?

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Diagram of a human head in profile showing the location of vocal organs and possible places of articulation for speech sounds, with labels for lips, teeth, tongue, palate, uvula, pharynx, and vocal cords, and numbered regions corresponding to types of articulation such as bilabial, alveolar, and velar.
phonetics Diagram depicting the location of human vocal organs and possible places of articulation used for speech.

Voiced sounds are produced through a mechanical process described by the myoelastic or aerodynamic theory of voice production.1

The process occurs as follows:

  • Adduction: The vocal cords are brought into a closed position by the adducting muscles.1
  • Air Pressure: Expiratory effort from the lungs drives air upward through the trachea against the undersurface of the vocal cords.1
  • The Cycle: Once subglottic pressure is sufficient to overcome the closing force of the cords, the glottis is forced open, releasing a puff of air.1
  • Elasticity: The reduction in pressure, combined with the elasticity of the glottis and the airflow, causes the cords to snap shut again.1

This cycle of opening and closing repeats rapidly, creating vibrations that result in voiced sounds. The frequency of these cycles determines the pitch of the sound, with higher frequencies producing higher tones. Unlike active muscular movements, this vibration is a passive mechanical phenomenon maintained by the airflow and the tension of the vocal cords.1