In 2019, Kim Hyuk Gun (김혁건), the vocalist of THE CROSS (더크로스), opened the "vocal organs" chapter of his doctoral dissertation with this point: phonation happens not only through breathing but through the interaction of the vocal organs and breathing. He then showed photographs he took of a medical laryngeal model — the outside and inside of the larynx and where the vocal folds sit.
This is the fifth part of the series. It sets out the structure of the place where the breath of Parts 2–4 arrives — the larynx and vocal folds — and how sound is made there.
01.Breath Alone Does Not Make Sound
The dissertation writes that a correct understanding of the mechanism of phonation requires an understanding of the larynx among the vocal organs. The larynx is an organ made of several cartilages, muscles and joints.
Breath is the raw material of sound, and the larynx and vocal folds are the device that turns that material into sound. If Parts 2–4 covered the material, Parts 5–8 cover the device.
| Part | Topic |
|---|---|
| Part 5 (this article) | The structure of the larynx and vocal folds; how sound is made |
| Part 6 | The balance of force between the vocal folds and the diaphragm |
| Part 7 | Chest (full) voice — the sound made with the folds together |
| Part 8 | Falsetto and registers |
02.The Larynx Seen on a Laryngeal Model
The dissertation's photographs of the larynx were taken by the researcher of a medical laryngeal model. The airway faces up and toward the back, and the larynx wraps around it like wings.
Opening the larynx and looking left and right inside the airway shows where the vocal folds sit. The vocal folds are divided into left and right, and they rub against each other to make sound waves. Looking down at the larynx from above, sound comes through the gap between the left and right vocal folds in the airway. That gap is the glottis.
03.The Muscles That Move the Vocal Folds
Among the muscles of the larynx, the cricothyroid and cricoarytenoid muscles and the cricoarytenoid joint act directly on the vocal folds and affect the sound. The dissertation sets out the muscles a singing student should know like this.
| Muscle | What it does | In singing |
|---|---|---|
| Cricothyroid | Lengthens the vocal folds front to back, raising their tension | Works when raising the pitch |
| Cricoarytenoid | Brings the vocal folds close together (adduction), leading them to touch | Uses the exhale to make the voice |
| Lateral cricoarytenoid | Brings the vocal folds close so that contact can happen | The ability to create and keep this state is very important in singing |
| Muscles above / below the hyoid bone (extrinsic laryngeal muscles) | Raise / lower the larynx | The position of the larynx changes the texture and size of the sound and the length of the vocal tract |
The dissertation names five intrinsic laryngeal muscles — the cricothyroid, posterior cricoarytenoid, lateral cricoarytenoid, thyroarytenoid and arytenoid — and explains that they raise and lower the pitch by controlling the movement of the vocal folds.
The height of the larynx also changes the sound. The position of the larynx affects the length of the vocal tract, which changes the length and overall area of the resonating space, and that in turn changes the character of the sound we hear. The dissertation introduces a study finding that phonating with the larynx lowered increased loudness and the vocal-fold contact rate compared with phonating with it raised. This is where the problem of chest breathing seen in Part 3 — the larynx rising along with the shoulders — shows why it works against the sound.
04.The Vocal Folds: 2.4 Centimeters and 1.7 Centimeters
The vocal folds are a very small organ, averaging 2.4cm in men and 1.7cm in women. The length and size of the vocal folds, which differ from person to person, are the main factors that set a person's range and tone.
| Vocal folds | Tone |
|---|---|
| Thick and long | A darker tone |
| Short and thin | A higher, brighter voice |
The vocal folds have three layers — mucosa, ligament and muscle — and of these it is the mucosa, rippling like a wave, that makes the sound. The dissertation writes that the principle by which the vocal folds vibrate has not been known for very long. The movement of the vocal folds was once explained as stimulation by nerve fibers, but after the "myoelastic-aerodynamic theory" was proposed, it became known that sound comes from vibration driven by the tension and elasticity of the vocal folds and by airflow.
05.A Balance of Closing and Opening
The dissertation sets out the making of the voice in three stages.
- Vibration of the vocal folds — The left and right vocal folds open and close periodically.
- Glottal sound — The steady, one-way airflow coming from the lungs into the glottis is turned into on-off pulses as the vocal folds open and close. The most basic frequency of this sound is the "fundamental frequency."
- Articulation and resonance — Passing through the path of the sound from the larynx (hypopharynx) to the lips — the vocal tract — it goes through resonance and articulation and becomes the human voice.
On how the vocal folds vibrate, the dissertation presents the aerodynamic theory as the current accepted account. With the two vocal folds brought together, the voice arises when the exhale from the lungs passes through the narrow passage called the glottis. The folds open and close as two forces take turns winning.
| Force that closes the vocal folds | Force that opens the vocal folds |
|---|---|
| The folds' own elasticity + the negative pressure created by air passing quickly through the narrow glottis (the Bernoulli effect) | The pressure the exhale creates below the folds (subglottic expiratory pressure) |
As the balance between the opening and closing forces shifts periodically, the glottal sound is produced and the fundamental frequency is formed. The title of the next part, "the balance of force between the vocal folds and the diaphragm," starts right here, inside the vocal folds.
06.Today's Practice
Turned into points to check while you practice, what the dissertation and the lesson highlight looks like this.
- The height of the larynx — As you raise the pitch while singing, check whether your larynx rises with it. The dissertation states that the position of the larynx affects the texture and size of the sound and the length of the vocal tract, and introduces a study in which phonating with the larynx lowered increased loudness and the vocal-fold contact rate (section 03; dissertation p.85).
- Seeing the vocal folds touch — Lesson Ep. 2 shows endoscope footage of the vocal folds coming together (video description). Check in the video what the cricoarytenoid in the table in section 03 does — bringing the folds together so they touch (dissertation p.84).
- Finding the places in the mouth — Use the same lesson to check where the hard palate, the soft palate and the back space (Jaw) are, as it explains them (video description). The soft palate comes up again in Part 9 · The Resonators.
The lesson to watch with this part is Season 1, Episode 2, "Head Voice." Its description lists vocal-fold closure seen through endoscope footage, photographs of the vocal folds and laryngeal cartilage, the hard and soft palate, and the back space (Jaw) and vowels. Head voice gets its own part in Part 13.
07.Where to Go Next
The structure that moves the breath is in Part 4 · Lungs, Diaphragm and Breathing Muscles, and how the vocal folds and the breath share the force on high notes continues in Part 6 · The Balance of Force Between the Vocal Folds and the Diaphragm. The hard rock and heavy metal high notes sung with these vocal folds can be heard in THE CROSS Band's Rock Covers. Lesson videos are in Korean.
Two bands of muscle around 2 centimeters long close and open — and there, breath becomes sound.