As a voice teacher, I often find myself explaining to students how the voice works and why it’s important to take good care of it. While it’s not necessary for all singers to know all the tedious details (muscle names, etc), a basic knowledge of how the voice works is important because it helps singers understand their instrument.
Sound is produced by the vocal folds (commonly called vocal cords), which are tiny muscles inside the larynx (aka “Adam’s apple”). They are about the size of a dime in women and the size of a nickel in men. They form a “V” shape, which can open or close, and when they are fully closed they block the airway to the lungs. (To experience this, try to lift something very heavy while inhaling or exhaling. It should be difficult if not impossible.) To produce sound (for speaking or singing), the vocal folds gently come together and vibrate as air is passing through. This process is called phonation.
The vocal folds stretch to become longer and thinner for high pitches, and thicken and shorten for low pitches. When the muscles of the larynx are trained to work together efficiently, the singer will be able to smoothly and evenly move throughout his or her range. Voice breaks and cracks are signs that these muscles are not working together effectively.
The vocal folds are covered by a delicate mucous membrane, which is an important part of the vibration that creates sound. This membrane moves in a wave-like rippling motion. It is very important for singers to drink plenty of water so that this membrane stays moist and does not dry out. A dry mucous membrane is much more susceptible to damage, including hemorrhages and nodules.
The sound produced by the vocal folds is different from the sound we hear outside of the singer’s body. At the source, it is a soft buzzing sound. As this sound passes through the throat and mouth, or resonators, it is filtered and amplified into the sound that we recognize as singing. This process is why things like jaw and tongue position and mouth shape are so important for singers: these things shape our sound, and a small adjustment can make a big difference.
There are some really cool videos on YouTube that show the vocal folds in action. Just search for “vocal fold stroboscopy” (this process uses a tiny camera and a strobe light to show the vibrations in slow motion).
If you are interested in a more detailed and scientific description of the vocal folds, watch this video from Anatomy Zone.