How Do the Vocal Cords Work?

All About Phonation

Jazz Singer

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Phonation is defined as vocalization. Vocal sound is created by the opening and closing of the vocal cords, caused by airflow from the lungs. Muscular resistance to the air pressure also determines sounds from breathy to pressed or pinched.

How the Vocal Cords Open and Close

Bernoulli’s principle explains why air opens and closes the cords. It is the same principle that keeps airplanes in the air. It states that slower moving air has more air pressure than faster-moving air. When the space between the vocal cords is narrow, it is similar to a spot on the freeway that goes from four lanes to one. Before the constricted area, cars build up and slow down. During the one lane opening, few cars slowly get through and speed up after the highway opens up to four lanes again. The same goes for air flow through the vocal cords; pressure builds up below the vocal cords when the space between them is narrow. Eventually increased air pressure bursts them open. Muscular resistance to Bernoulli’s principle manipulates sound produced by the laryngeal activity.

Use Paper and Lips to Replicate Action of Vocal Cords

Take two sheets of paper and place them vertically in front of your mouth. Blow air forcefully through them. You may think the air will push the papers apart. It causes the papers to flap together, which is an obvious representation of how the vocal cords work inside the larynx. Another similar activity is to buzz the lips, by keeping them loose and breath flowing. If you add pitch to the buzz, notice the lips elongate and loosen on lower notes and shorten and tighten on higher ones just like your vocal cords.

How the Vocal Cords Produce Loud Sounds

Notice the two vibrating papers make very little sound. Vocalization, however, makes a significantly louder sound because of the resonating chamber of the vocal tract in the human body. Each vocal cycle creates a puff of air produced by air pressure below the vocal cords causing them to suddenly open. Each air puff is like a tap on a drum. It sends a wave down the vocal tract causing it to vibrate. The rate at which the vocal tract vibrates determines pitch. So, 440 puffs of air per second create the pitch A above middle C. The frequency is referred to as 440Hz or hertz, which means cycles per second. The vocal tract can also be adjusted to create a louder or quieter sound.

Where the Vocal Cords Are Located

The larynx often referred to as the voice box, is located on the neck where the Adam’s apple is. It houses and protects the vocal cords. Many muscles within the larynx aid in vocalization, but the vocalis muscle provides the main mass of the vocal cords. Laryngeal activity is another and possibly more accurate way to refer to vocalization because it refers to all muscles involved rather than just the vocal cords.

How Knowledge of Vocal Cords Can Improve Vocal Tone

With knowledge of how the vocal cords work, singers can find their breath threshold. Breath threshold is the perfect balance between air energy caused by the Bernoulli Effect and muscular resistance to that energy by the vocal cords. The product is the loudest, most efficient and beautiful vocal sound each singer is capable of. If you sound pressed, then you are using too much muscular force to slap the vocal cords together. If you sound breathy, then you may not be closing your vocal cords together efficiently. To find your breath threshold, sing one note on 'ah' as breathy and quietly as possible. Sing the note again just as breathy, but a bit louder. Repeat this process until you cannot sing any louder. Breath threshold is the point just before applying more muscular effort to sing louder does not add volume.