Resonance: The Science of Sound
Let’s take a quick look at how sound is itself is produced so we can then see how sound can be shaped and enhanced. To begin with, we must bear in mind that all sound is produced by vibration. All sound, whether it is a fire siren or my hand rubbing across my jeans. If something vibrates fast enough within the medium of air, it will produce sound. Even my hand, if shook back and forth fast enough, would produce an audible pitch. The reason for this is that as an object passes quickly through air, for a very brief moment it causes a hole where there is no air. We call this hole of non-air a vacuum. The air surrounding this vacuum quickly tries to fill in this hole, which in turn creates a rippling effect known as a sound wave.
Therefore, sound that travels through air can be viewed as a hole being filled causing another hole that is filled and so on. This wave of energy enters into our ears and is ultimately interpreted as sound. The faster the vibration the higher the pitch becomes. This is known as the sound waves ‘rate’.
The volume of the pitch is another story. The volume or loudness of the pitch is controlled by how much air is moved around. This is the sound wave’s amplitude. The more air that is displaced the greater its amplitude, and the louder the pitch will be. The tonal quality of my hand waving back and forth a few hundred times a second may not sound so appealing as of yet. Its’ tone needs to be shaped in some manner by adding some form of EQ (equalizer) which will raise or lower the volume of the different frequencies of my hand’s tone and then a nice thick layer of resonance (echo) which will enhance it.
In the natural world there would be many different elements that can shape and enhance my hands tone. The tone will vary based on whether my hand is open or closed, or tight or lose. The size, shape and orientation of the room that I am in will alter the tone. If I am wearing a watch, the different density of the metal in my watch would cause it to resonate differently than my skin, and the two combined together would sound different than if heard separately. Maybe, the metal has a more piercing tonality and my hand itself has a slightly darker tone. So hopefully you can see that just a simple examination of tone has us discussing words such as rate, amplitude, and frequencies. Again, many small concepts rolled into one.
Often times when I am teaching these concepts is use a tuning fork to demonstrate. This device was the only method of tuning instruments such as guitars and pianos until the marriage between technology and music surfaced and gave us electronic and digital instrument tuners.
Tuning forks are still a great way to teach basic facts about sound energy. When I strike the tuning fork it sets the thongs into vibration. I happen to have a tuning fork that vibrates at the incredible speed of 440 vibrations per second. This speed is what we define as the note (or pitch) A. When we hear a guitar for instance playing this note it is vibrating 440 times per second. If I start to sing that note, my vocal folds are also vibrating 440 times a second! Amazingly, if I sing an octave higher my vocal folds would be vibrating 880 times a second, which is exactly double the original speed. This is why octave’s sound exactly alike but are higher or lower in pitch.
When I strike my tuning fork and set it into vibration, I don’t really hear too much. That is… until I set the handle end of the fork on a hard surface. Incredibly, the tuning fork has seemingly increased its overall volume. Or has it? I mean, I can hear it better than when I first struck it. What happens is what we call sounding board resonance.