The vocal folds are positioned inside the larynx, also known as the voice box. This is where sound is produced. The vocal folds are positioned above and across the windpipe (trachea). When we inhale and exhale without sound the cords are open and air passes between them in and out of the lungs. We can choose to bring the vocal folds together as we exhale and this makes their mucous membranes vibrate to produce sound.
Anatomy of the larynx
The larynx consists of numerous parts. The thyroid cartilage, positioned around the front of the vocal folds, serves to protect them and creates the pointed structure you can feel in the front of your neck (the ‘Adam’s apple’). Inside this pointed structure, the vocal folds are attached together at the front. They are positioned above and across the windpipe. At the back, the two vocal folds are each attached to an arytenoid cartilage. The arytenoid cartilages sit on the rim of the cricoid cartilage which is the top of the windpipe. It is, in fact, the arytenoid cartilages that move from side to side, opening the vocal folds when we breathe, or closing them when we speak or sing. The arytenoid cartilages are also able to tilt up or down, thereby altering the length of the vocal folds. When the vocal folds are stretched and lengthened the pitch is raised.
Above the vocal folds are the false folds (ventricular folds).They consist of ligaments, muscles and glands. Outside this is a cover of mucous membrane like the rest of the inside of the body. This mucous membrane is not as flexible as that of the true vocal folds.
The epiglottis is attached to the back of the thyroid cartilage at the angle just below the notch (superior thyroid notch) and above the vocal folds. When we swallow, food slides down over the tongue and the epiglottis tilts backwards. This helps prevent food passing into the trachea (windpipe) which would cause us to choke. Once the food has passed through, the epiglottis returns to its original position, standing up from the thyroid cartilage. The hyoid bone is positioned at the very top, attached to the thyroid cartilage (the hyoid bone is not shown on the figure above).
Sound is vibration or pulsation of air. The faster these pulsations are, the higher the pitch. Pitch is defined by the number of pulsations per second, also known as Hertz (Hz). It is the vocal folds and their mucous membranes that create the pulsations with which we speak or sing. The note A4 is equal to 440 Hz, so to sing A4 the mucous membranes of the vocal folds must vibrate 440 times every second you sing this note!
Vibrations of the vocal fold and volume
Each vocal fold consists of a vocal ligament which is lined by a moveable mucous membrane. This membrane creates sound through its rapid opening and closing movements (vibratory cycle), creating vibrations in the air or sound waves. The larger the vibrations of the air, the more powerful the volume.
The vocal folds form a narrowing of the air passage (a). When the air stream passes through this narrowing, a partial vacuum is created, thus bringing together the membranes of the vocal folds (b-d). (The same effect occurs when a bus passes you at great speed, you can get sucked in behind it). The movement where the membranes close is called the ‘closed phase’ (e-i). The closed phase begins with a suction movement at the bottom edge of the vocal folds and moves upwards in a rolling motion. In the closed phase the flow of exhaled air is momentarily stopped which creates an increase in pressure beneath the vocal folds. The upwards rolling motion ends with the vocal folds separating when the pressure is released (j). Now the cords have completed one pulsation/vibration or vibratory cycle and are ready for the next one. This repeated interruption of the air stream by the mucous membranes coming together creates a series of pulsations known as a ‘sound wave’.
For the note A4 the mucous membrane vibrates at 440 pulsations per second, and this requires a very stable speed of the airflow. By increasing the airflow, the vacuum strengthens and the mucous membranes go into bigger movements – this creates bigger volume. If a singer at a certain point exhales so strongly that it is forcing the membranes apart, it will consequently impair the refined vibration, so to obtain a note the singer has to bring the cords together by uncontrolled constriction. Now the singer gets into problems. The uncontrolled constriction limits the movement of the cords which thereby limits the volume. This is what is called ‘forcing’ the voice and causes much damage.
Consequently there is a limit to how fast the air should be let out while singing. Above this limit the voice does not work efficiently. Even at very powerful volumes the speed of the air stream should not be so fast that it no longer feels like you are holding back the air. This is why correct singing and speaking always has the sensation of holding back the air. This control of the exhalation is achieved by using support.
To keep the speed of the air within the range where the vocal folds can move freely is a balancing act and requires support energy. This is even more applicable when you reach the extreme ranges of voice and volume. On very powerful tones the danger of ‘forcing’ is great. On very quiet tones it is often more difficult to avoid uncontrolled constriction, and here even a minor change in the speed of the air may interrupt the small vibrations. So the work of supporting powerful and quiet tones is both physically and technically demanding. It is not enough for the singer to be technically skilled, s/he should also be in excellent physical shape and have great stamina.
The work of the vocal folds is a very refined process and it does not take much to spoil these delicate, rapid movements. The aim for singers is to give their vocal folds the best possible working conditions, by controlling the outflow of air and preventing uncontrolled constriction in the throat.
A solid support technique is vital otherwise the membranes of the vocal folds grow weary from the constant pressure of out-flowing air. A consequence of this might be tired, swollen vocal folds vibrating irregularly. It is very strenuous for the muscles of the vocal folds to keep them together while there is constant pressure from out-flowing air. This could lead to uncontrolled constriction around the vocal folds. This uncontrolled constriction might lead to straining or incorrect use of the vocal modes which eventually causes hoarseness and an inability to reach a desired pitch.
Regulation of the pitch
When we produce high and low notes the vocal folds are tightened and relaxed by the thyroid cartilage and the cricoid cartilage approaching each other, and the movements of the arytenoid cartilages and a number of muscles. When the vocal folds are stretched they vibrate more rapidly and produce a higher note. On low notes the vocal folds are relaxed, become short, and vibrate more slowly. This is how pitch is regulated.
Movements of the larynx
The position of the larynx varies depending on whether you are producing high or low notes. If you want free and unhindered notes you MUST allow the larynx to rise on the high notes and to lower on the low notes. The larynx will always to some extend be raised on high notes and lowered on lower notes.
If a singer maintains the larynx in a much too low position, high notes become unreachable. In order to reach the notes you want, it is essential NOT to fix the position of the larynx but to let it reach the right position for the pitch. Then later you can raise or lower the larynx a little within the right position for the pitch, in order to colour the sound lighter or darker.
- The vocal folds are positioned inside the larynx above the windpipe.
- When we inhale the cords separate, but when we sing or speak they are pulled together.
- Sound is vibration of the air. It is the vocal folds and their mucous membranes which make these vibrations; the faster the vibrations, the higher the note. For example at the note A4 our vocal folds and their mucous membranes are vibrating 440 times every second!
- The vocal folds stretch on high notes and relax on low notes.
- The larynx rises on high notes and lowers on low notes.