This transfer of vibrations between any two adjacent atoms or molecules in the gases that make up the air is known as ‘sound.’ The energy in a sound event, for example, someone toning, expands away from the mouth and nose equally in all directions as a bubble.
This sound bubble naturally expands at the speed of sound, which is 768 miles an hour at 68 degrees F (20 degrees C) at sea level, and its outer ‘surface’ is in a state of radial pulsation or oscillation, meaning that it is expanding and contracting.
The bubble’s pulsations are the same as those created by the vocal folds in the larynx. The pulsations of the bubble are the sound. At this point, you might be thinking, “But what about sound waves?” The model of ‘sound waves’ is incomplete and a misnomer because it refers to the graphical representation of the mathematical law of sound energy. While the term ‘sound waves’ is correct in its graphical representation, it is not how sound propagates or travels.
Sound Bubble Versus Sound Wave
The concept of sound as a wave is simply a label used to describe the fact that sound bubbles pulsate in and out rhythmically. It is this pulsation of the bubble’s outer surface typically illustrated as a wave-like graph. Put differently, when teachers and scientists describe sound as a wave, they are referring to its rhythmic pulsation depicted graphically, not its actual shape in space. The result of this confusion is that most people incorrectly visualize sounds wiggling their way through the air rather than visualizing beautiful, shimmering sound bubbles.
A sound bubble in the illustration above is halved to see its internal structure. The sound event that created the bubble is in the center. All sounds contain high and low-pressure areas called compressions and rarefactions.
The illustration (on the left) shows these areas as dense blue hemispheres for high pressure and pale blue hemispheres for low pressure. If you study the drawing closely, you will see dotted lines rising out of the bottom half of the bubble and connecting with a wave graph in the middle. This illustrates clearly where the term ‘sound waves’ comes from: the wave-like graph of sound is a mathematical representation of an actual sound bubble.
Many scientific textbooks illustrate the spherical nature of sound, even though they continue to use the term ‘sound waves’ for acoustic energy that has a bubble-like space form. A good example is the Master Handbook of Acoustics. The chapter heading on page 83 is: “Sound Waves in the Free Field,” yet on page 85, there is a drawing showing the spherical nature of sound.1
Holographic Sound Principles
To build a deeper foundation of understanding, when sound travels through air, every atom or molecule in the path of the expanding sound bubble is involved in passing on the sound vibrations. It is like when a long row of set-up dominos bump into each other and set off a chain reaction of movement. In the air, the vibrations that originate with the atoms and molecules in direct contact with the sound source pass on their vibrations to their nearest neighbors, and the chain reaction begins, spreading out as a bubble of sound.