Imagine a world full of waves vibrating around you, all of them different sizes, shapes, and colors. Now close your eyes and focus on the sounds that you can hear. You can probably hear something mechanical, like an air conditioner, or your own breathing. Maybe you hear music, children laughing, cars driving past, or sirens in the distance. The world you imagined is around you already; it is the world of sound. Now let’s look at how this world is created.
All sound is made by movement. Rapid movement back and forth causes air to be pushed away. As the object moves back, the air does not fill in the space it was pushed from and a small vacuum is created, making a wave shape. These waves are sound.
If you take a rubber band and stretch it over your fingers, you can test the way that sound changes. Plucking a loose rubber band will produce a lower sound, while a rubber band that has been stretched tight will make a higher sound. Guitar strings work this way. The looser and thicker the string, the slower it can vibrate. These slow vibrations make the low sounds like a bass guitar. A tighter, thinner string cannot move has far as it vibrates. Its vibrations are tight and fast. This makes higher notes. On a guitar, the length of the strings can be changed by the player’s fingers. A shorter string vibrates more quickly than a longer one, causing a higher sound.
Since sound waves are literally caused by compressed air, it is easy for loud noises, the really strong waves, to damage hearing because of the increased pressure. In fact, sound waves can also be called pressure waves.
People who go to concerts might notice a pressurized feeling in their heads if they pay attention. How does the sound get that loud? An electric guitar by itself, not hooked up to speakers, is pretty soft. Now we are talking resonance and amplification.
An acoustic guitar is bulkier, right? It has a hole right under the strings where they are plucked. The air inside the acoustic guitar captures the sound and the wood at the back reflects the waves back stronger. This use of empty space and a sound reflector is called resonance. The sinuses in the human head do the same thing. The empty sinus space and the bones of the skull resonate our voices to make them louder.
The design that is common in most electric guitars is that of a solid body: no extra space. That is why an electric guitar sounds soft all on its own; it has no resonance. That is where the speakers come in to play. The vibrations of the strings on an electric guitar are picked up in the solid body of the guitar and passed electrically to speakers. These speakers mimic the guitar’s sound waves while making the waves bigger and stronger and, therefore, louder. The increase of the strength of a sound wave is called amplification.
Vocal chords vibrate like guitar strings. Clapping hands together creates a single sound wave. Go explore the world of sound!