By Angel Lyn Horner
Studying the theory and foundations of sound physics includes concepts of sound waves. A sound wave is a vibration, usually mechanical, that travels through a medium or middle point between extremes. As an object vibrates, waves are the result. The molecules around begin to oscillate, producing pressure changes that multiply or propagate through the medium. These waves require an actual physical medium, such as air, water, or solids, to journey or travel through. This is quite different from electromagnetic waves.
Sound waves are from vibrating molecules or objects. As the vibrations occur, movement of back and forth and side to side, alternating low and high pressures emerge, creating compressions, which create a pressure variation that moves out from the source. These are audible waves of pressure that we can hear and also perceive them in bones and skin. All sounds affect our tissue and our body, so really we can “hear” with our entire body. If we apply this to physics, we would never have a sound wave without movement. The vibration of a sound is transmitted to our sensory organ of hearing, the human ear, and then recognized in the nerve centers. These are electrical signals that are processed by the brain. A disturbance will produce vibrations in the air, such as the horns blowing in traffic in New York City! Our ears quickly pick up and process that disturbance via the sound waves produced by many horns. As this information is processed, it can give one a headache and make them feel anxious for sure!
As the vibrations occur at regular intervals, which is a fixed measurement or unit of time. The cycle of the motion becomes frequent, creating a “frequency”. The motion must reach 20Hz to become audible, or hear it. Infrasound is below the audible range, and ultrasound frequencies are above what the human ear is able to register, 16000-20000 vibrations a second, so they are not audible. Even though they are not audible, they may affect tissue, even causing damage. In medicine and physiotherapy, there are recommended doses of ultrasound, not exceeding the maximum dose for safety reasons and to avoid the potential for injury as these waves are absorbed into the body (1). As the sound travels and the audible vibrations reach the human ear and are delivered, this is referred to as “loudness.” This is the amplitude.
As the variation in the vibration changes, the faster it is, the waves are denser and the “pitch” becomes higher. It has been documented that neural networks actually track musical structure, so therefore the pitch affects the brain networks (2).
You can feel and listen with “the third ear” when taking Chinese Medical diagnostic pulses on an individual and feel and “hear” a change in amplitude (loudness)on the radial artery as you “listen to the pulse”. This is an example of hearing through and with the human body. (2).
When the vibrations that propagate sound waves, and then provoke additional vibrations on another object, passing through the medium, making them vibrate at the same rate, this is resonance. It is when one vibration influences another. This can be demonstrated using tuning forks, two of the same frequency, one with a different frequency. Strike one, and its twin fork will vibrate if placed near it. The one with a different frequency will not activate, because it does not resonate not being the same frequency. This is different from the Schumann Resonance of the earth, which is electromagnetic standing waves that are excitable by lightning, creating peaks of ultra-low frequency electromagnetic waves.
In the conclusion, the physics of sound as we know it is fascinating, a blending of wave motion with the audible perception of a sound wave and the ability to affect the human brain and human physiology. We only have to look to the sounds of nature to see their effect on humans, both physical and psychological (4).
- Moyano DB, Paraiso DA, González-Lezcano RA. Possible Effects on Health of Ultrasound Exposure, Risk Factors in the Work Environment and Occupational Safety Review. Healthcare (Basel). 2022 Feb 24;10(3):423. doi: 10.3390/healthcare10030423. PMID: 35326901; PMCID: PMC8954895.
- Janata P. Brain networks that track musical structure. Ann N Y Acad Sci. 2005 Dec;1060:111-24. doi: 10.1196/annals.1360.008. PMID: 16597758..
- Bilton K, Hammer L, Zaslawski C. Contemporary Chinese pulse diagnosis: a modern interpretation of an ancient and traditional method. J Acupunct Meridian Stud. 2013 Oct;6(5):227-33. doi: 10.1016/j.jams.2013.04.002. Epub 2013 Apr 24. PMID: 24139459.
- 4 Song I, Baek K, Kim C, Song C. Effects of Nature Sounds on attention and physiological and psychological relaxation. Urban Forestry& Urban Greening, 2023, August: Vol 86,127987. https://doi.org/10.1016/j.ufug.2023.127987
