The Dynamics of Vocal Fold Vibration
Phonation is the process through which the vocal folds, located in the larynx (or voice box), vibrate and produce sound. This complex action lies at the heart of how we generate the sounds integral to speech and singing. Understanding phonation involves the interplay of muscle action, airflow, and tissue elasticity, as described by the myoelastic aerodynamic theory of vocal fold vibration.
The Myoelastic Aerodynamic Theory
This theory explains how the vocal folds vibrate not through muscular contraction alone but by a combination of muscle elasticity (myoelastic) and air pressure and flow (aerodynamic). When we decide to speak or sing, our brain signals the muscles in the larynx to bring the vocal folds together, a process known as adduction. As breath is expelled from the lungs, it passes through the closed vocal folds, building up subglottal air pressure beneath them.
Once the subglottal air pressure is sufficient, it forces the vocal folds apart, releasing a puff of air into the vocal tract and creating a sound wave. However, because the vocal folds are elastic, they snap back to their original position, allowing the cycle to repeat rapidly. This vibration happens so quickly that it can occur hundreds of times per second, depending on the pitch of the sound produced.
Modes of Vibration
The vocal folds can vibrate in various modes, depending on factors like tension, mass, and subglottal pressure. These modes include modal voice (used in normal speech), falsetto (a higher, lighter register), pulse register (a low, creaky sound), and whistle register (the highest notes). The mode of vibration affects both the pitch and quality of the voice that is heard.
Subglottal Air Pressure
Subglottal air pressure is the driving force behind vocal fold vibration, determined by the amount of airflow from the lungs and the resistance created by the vocal folds. Balancing this pressure is key for controlled phonation; too little pressure and the vocal folds won’t vibrate effectively, too much and the voice can become strained or the vocal quality harsh.
Semi-Occluded Vocal Tract Exercises
These exercises are designed to train and maintain efficient phonation by partially blocking the vocal tract, which creates back-pressure that helps the vocal folds to vibrate with less effort. Common examples include humming, lip trills, “buzzy” voiced fricative consonants such as /z/ or /v/, or voicing through a straw. These exercises can improve vocal fold closure, reduce the physical effort needed to phonate, and promote optimal voice use with minimal strain.
Phonation is a delicate balance of muscular coordination, breath control, and acoustic phenomena. Understanding and practicing efficient phonation techniques allow for a voice that is both resilient and expressive, capable of meeting the demands of varied performance circumstances.
Resources
Videos
The Process of Phonation:
Vocal Folds in Action:
A Beatboxer and an ENT: