How does your voice get louder?
The vocal cords (that's the correct spelling) are two folds of body tissue right at the top of your larynx (windpipe). Before today, I was very misinformed about these things. I thought the word was spelled chord, like the musical chord, and that the vocal "chords" looked like a harp -- strings that vibrated as air blew through them. Armed with my lack of knowledge, I got in an argument about how yelling works and I said it was caused simply by pushing more air through the "chords". The person who I argued with completely disagreed, saying that it was the muscles themselves that somehow increased the volume. I decided to find out.
Let's start at the mouth opening. This is the entryway to two important pipes, the one used for eating (the esophagus) and the one used for breathing. If we start at the back of the throat and slowly move down, we encounter where the two pipes separate. Right above the breathing pipe is a flap of tissue known as the epiglottis, which covers the breathing pipe when you're eating or drinking.
We decide to go further into the breathing pipe. Past the epiglottis, we see a set of two folds of tissue that don't move too often. These look like vocal cords, but are actually called the false vocal cords or ventricular folds (or vestibular folds, they have a lot of names). They're not used, unless you're singing death metal. Below those we find the real vocal cords (also folds of tissue) and muscle that connects to them. If you had a top down look, you'd see an opening with what looks like eyelids coming from the sides instead of the top and bottom.
Finally, if you went further down past the vocal cords, you would find yourself in the trachea. This is the part of the pipe that connects all that stuff above (called the larynx) to the lungs.
Getting chords from the cords
The vocal cords are essentially in two different positions. They are further apart when you are breathing so that you can let more air through to the lungs and closer together when you speaking or producing sound. This is because when you breathe quietly, you let air in slowly and breathe it out slowly. But when you speak, you breathe in much more quickly and exhale for longer.
Speech and other sounds are produced by your vocal cords oscillating. They alternatively move closer and further together in a controlled motion that comes from the interplay of the muscles attached to the vocal cords and the non-muscular tissue structure. This oscillation blocks and opens the airway, changing the air pressure and creating different types of sound.
Sidenote about sound
Now that I'd corrected my misinformation about how vocal cords make sound, I wanted to focus on my real question: How does a voice get louder and softer? But first, what is loudness?
Sound (literally) does not exist in a vacuum. We hear sound when there is a periodic oscillation of air pressure -- particles in the air get closer together and further apart in a pattern -- and that air hits our eardrum. This air compression and expansion (or change in air pressure) happens at an atomic level, but our eardrum is sensitive enough to perceive a lot of it.
More formally, sound waves are longitudinal. In general, longitudinal waves are the periodic compression and expansion of particles in a medium. Another way to think of them is that the way the particles move is in the same direction of the wave. This is different from waves in water, which are transverse waves. The water moves perpendicular to the direction of the wave, which is why you can see ripples.
When the vocal cords oscillate and change the air pressure, they create a complex sound -- a combination of many different types of waves. The pitch of the sound is related to the frequencies of the waves. But the sound's unique quality, known as timbre, is related to the shape of the wave itself. For the voice, this depends on every person's unique vocal cords and how their vocal muscles move.
To be continued in a later post...
- Foundation of Voice Studies, Kreiman and Stidtis (https://onlinelibrary-wiley-com.ezproxy.lib.utexas.edu/doi/pdfdirect/10.1002/9781444395068)