Vocal anatomy and voice production physiology are areas of knowledge I continue to seek clarification in. As a young singer, an inured singer, and now a singing voice-specialized speech pathologist, I aim to continue to teach myself and to make it simple for anyone curious with the following information about what vocal cords are, what breath has to do with phonation, what makes pitch and volume, and how our throat and facial filters influence vocal sound.
What Are Vocal Cords?
Humans have 2 bands of tissue in their throat that open for breathing and close to create sound. We call them either vocal folds or vocal cords. (Chords are musical notes, not the tissues.) Vocal cords/folds sit on top of the windpipe (also called the trachea) and provide safety when they close so you can hold your breath when swallowing. They also slam together when you cough or throat clear. They close completely and flap together to vibrate when you make noise to speak, sing, grunt, scream or cry. This act of vibration for vocalization is called “phonation.”
These vocal cords sit within a structure inside your throat called the larynx. The larynx is made up of 2 main house cartilages (and many other structures inside), the thyroid and the cricoid, that create the space for the vocal cords to sit.
What About Respiration?
There is a need for fuel in any mechanical system, and the breath provides that fuel to the voice. We use abdominal and lung muscles to control how quickly or how slowly we allow air to leave through the vocal cords during vibration. Respiratory strength and endurance is key to making the vocal subsystems coordinate for control of sounds, as well as coughing.
The diaphragm is a dome shaped skeletal muscle that sits below the lungs and tenses during inhalation (breathing in) and relaxes during exhalation (breathing out). Misinformation has been widely spread about us having isolated control (volitional specifically) of the diaphragm for proper “breath support,” but the diaphragm is a passive action structure and you can’t “contract” or “relax” it independently on command like you would furrow your brow, squeeze your abdominal muscles or tighten your bicep.
You can train respiratory endurance and strength with certain exercises and devices like pressure threshold trainers that can target inhalation or exhalation. Weakness in breath control, endurance and strength can result in a decline in vocal loudness or a change in vocal quality.
What Influences Pitch?
Vocal cords have a certain size naturally, comprised of mass and weight. Larger and heavier, fatter tissues will vibrate at a slower rate of speed creating a lower pitch. Smaller, less heavy vocal folds will vibrate at a higher rate of speed creating a higher pitch. Pitch is another word for frequency of those collisions and is measured in Hz (Hertz). Hormones influence the mass and weight as vocal cord tissues grow, determining which pitches a person has access to when talking or singing. Puberty influences the amount of size/weight changing hormones for these tissues and causes a lowering of Hz for all humans exiting childhood, some voices lowering more than others.
Another way to influence pitch is the active motion of lengthening or shortening the vocal cords. When you stretch the vocal cords to an elongated posture, they stiffen and increase in pitch/Hz. Compressing or making them shorter in posture creates a lower pitch/Hz.
What Influences Volume?
Volume for voice production is more specifically defined as intensity and measured in decibels (dB). We can influence our vocal intensity by how hard we squeeze the vocal folds in proximity to one another during vibration, as well as how we handle the pressure below the vocal cords and how much air we do (or do not) allow to pass through the vocal folds during vibration. The longer the vocal folds stay closed during each phase of a vibratory cycle, the stronger the vocal sound production will be. The more complete the vocal cord closure pattern is (i.e. the contact that the vibratory edges achieve during vibration), the louder the vocal intensity will become as well.
Volume, measured in dB, can also be influenced by how rich and robust an acoustic signal is. By modifying the resonating cavity shape and height within the throat, the sound produced by the vocal cords can obtain harmonics that multiply one another. This is why certain vocal sounds can be heard over loud musical instruments with the vocalist feeling little to no effort because the acoustic phenomena is creating the dB increase.
This means you don’t have to rely solely on “surface area slapping” to generate the intensity of vocal signal you desire. You can play with throat shape and pitch to achieve a vocal sound that creates a rich and robust sound, feels easy to create, but does not rely on mostly mechanical forces to generate that intensity.
What is the Filter?
The air from your lungs sets the vocal cords into motion, called vibration. That vibratory sound travels through the spaces in your throat and out through 2 exit routes: mouth and nostrils. The spaces within your throat, mouth and nasal cavities are called resonant cavities.
How you shape these cavities affects how your voice sounds. Large-sized cavities with a lot of space (like when you yawn) create a low, deep and large sound. Singers sometimes describe this sound as dark or back-focused. Not all singers use the same laryngeal height for the same singing style. For instance “belt” can be made with a high larynx as well as a lowered laryngeal posture in some singers. Small-sized cavity shapes (like when you squeak or make baby talk noises) create a tiny, small sound. Singers sometimes describe this sound as bright or piercing.
The filter (combined with the size, length, and elongation of the vocal folds) influences the sound signal to create multiple formant frequencies and harmonics. The more symmetrically the vocal cords vibrate, the less chance they leak air and the less noise will be present in the sound signal. Our ears perceive symmetrical movement to be clarity in the voice quality. The more noise in a sound signal, like from breathiness or asymmetrical vibration patterns, the more disturbed the sound signal will be and the voice will sound rough, breathy, or aphonic.
I hope this blog was helpful. Here are some references you can read and some of my materials you can download instantly off my website.
- DIY Foam Larynx Model Patterns (2 patterns to print and create your own models; 1 moves)
- Voice Disorder Flipbook & Sheets (42 Printable sheets (English & Spanish), Printable flip book)
- Voice Disorder Poster (PDF file to print to ANY size on ANY type of poster material)
- Fogarty, M. J., Mantilla, C. B., & Sieck, G. C. (2018). Breathing: Motor Control of Diaphragm Muscle. Physiology (Bethesda, Md.), 33(2), 113–126. https://doi.org/10.1152/physiol.00002.2018
- Lovetri, J., Lesh, S., & Woo, P. (1999). Preliminary study on the ability of trained singers to control the intrinsic and extrinsic laryngeal musculature. Journal of voice : official journal of the Voice Foundation, 13(2), 219–226. https://doi.org/10.1016/s0892-1997(99)80024-1
- Rosenberg, M., & LeBorgne, W. (2014) The Vocal Athlete: Application and technique for the hybrid singer. San Diego, CA: Plural.
- Titze, Ingo (2000). Principles of Voice Production. National Center for Voice and Speech
- Zhang Z. (2021). The Physical Aspects of Vocal Health. Acoustics today, 17(3), 60–68. https://doi.org/10.1121/at.2021.17.3.60
About the Author: Kristie Knickerbocker, MS, CCC-SLP, is a speech-language pathologist and singing voice specialist in Fort Worth, Texas. She evaluates and rehabilitates voice, upper airway disorders and swallowing at her private practice, ATEMPO Voice Center, and lectures on voice science internationally. She is a classically trained mezzo soprano with a minor in vocal performance from Texas Christian University. She has collaborated on and authored multiple peer reviewed published research articles about her community-based voice specialty clinic. She continues to develop a line of instantly downloadable voice assessment and voice therapy materials on TPT or her ATEMPO voice center website. Follow her on Pinterest, on Instagram or like her on Facebook. Kristie is a founding member and co-owner of The Confident Clinician Cooperative and mentors on voice, upper airway, business and private practice through www.confidentclinician.com.
