Luke Holm earned bachelor degrees in English and Philosophy from NIU. He is a middle school teacher and a creative writer.
What is Sound?
If you’re here because of a Simon and Garfunkel song, stick around for a minute. While the duo sang about the dangers of ignorance and apathy in relation to communication and reform, they never actually explained a true definition of silence. This left me wondering, “What is the sound of silence, and what effect does silence have on the human brain?”
Before we discuss what silence is, it’s important to define what sound is and how sound is created. Sound is produced when an agent emits energy in the form of a vibration (atoms moving back and forth quickly). This vibration forces a medium, such as air, liquid, or a solid, around the catalyst to vibrate, and the moving air carries the emitted energy in all directions. The moving air is actually a sequence of atoms squishing together in some areas (compression) and stretching out in other areas (rarefaction).
This vibration produces a definite pattern called a sound (sonic) wave. The bigger the sound wave, what is called high amplitude or high intensity sound waves, the louder the sound. Something with higher amplitude, also referred to as high frequency, produces more energy waves per second than something with lower amplitude. This is why people hear a difference in pitch between musical chords, the range of voice ranging from soprano to bass, or the difference between fundamental sound compared to higher-pitch sounds such as harmonics and overtones.
The energy produced works together to create unique shapes in the sound waves, resulting in what is perceived to be different types of sound. Furthermore, some sounds dissipate more quickly than others. As atoms within the air lose their ability for compression and rarefaction, different sounds are created. Consider the way a flute sound dies quickly in comparison to that of a piano key. These variations are marked differences between the frequencies and amplitude of the sound wave; measured thusly as Decibels (dB).
The push and pull of energy or waves is what people oftentimes refer to as vibration. When there is an audience present, such as a human, animal, or an audio-input device, the vibrations are gradually converted into electrical signals that can then be interpreted into sound. In a human ear, the funnel-like structure of the outer ear canal (pinna) collects the sound waves within the air and causes them to vibrate the eardrum. Sound vibrations then move through an intricate set-up of three tiny bones (ossicles) called the hammer (malleus), anvil (incus), and stirrup (stapes) toward the inner ear and cochlea. The sound vibrations cause fluid in the cochlea to move, which causes the hair cells to bend within the inner ear. The hair cells create neural signals that are picked up by auditory nerves. The auditory nerves translate the vibrations into electrical signals that are then interpreted by the brain.
Therefore, sound is expressed in two different ways. One way is a physical process which consists of energy moving throughout a medium. The other is a physiological or psychological process which occurs within the perceiver, that which is influenced by the physical process, who converts the energy into sensory experiences oftentimes referred to as noise, speech, or music.
Depending on the medium through which it is passing, sound moves at various speeds. This means that there is no true speed of sound, as the measured speed depends on the density of the medium through which it travels. Sounds travels more quickly through solids than it does liquids, and faster in liquids than it does gases. For example, sound travels about fifteen times faster in steel than it does air, and about four times faster in water than in air. In air, sound travels more quickly when it is near the ground and moving through warm air, and more slowly when it is higher up and moving through cold air. Furthermore, sound travels about three times faster in helium gas than normal air because helium is less dense. This is why people who breathe in helium talk with a high-pitched voice for a short while; the sound waves are traveling faster and with a higher frequency.
Due to the fact that sound is a vibration passing through a medium such as gas, liquid, or a solid, there is no place on earth that is actually silent (aside from a laboratory induced vacuum). The only place representing true silence is space, since space is a vacuum without a medium through which sound can pass. The first person to discover that sound needs a medium to pass through was an English scientist by the name of Robert Boyle. He conducted an experiment in which he set a ringing alarm clock inside a glass jar and then sucked all the air of the jar with a pump. As the air gradually disappeared, the sound died out because there was nothing left in the jar for the sound to pass through.
What do Deaf People Hear?
Understanding how sound is translated into electrical signals within the brain, a person can come to understand why people might be or become deaf. A person who is deaf, or someone with a hearing impairment, has a problem with one or more parts of their ears, the nerves within the ears, or parts of the brain interpreting sound vibrations. There could be many instances which result in someone being deaf; ranging from birth defects, severe illness, physiological trauma, or trauma resulting from long, repeated exposure to loud sounds.
Just because a person is deaf, though, doesn’t mean that they don’t experience a sensory stimulus that some might consider sound. Typically, for people who are deaf, “hearing” is defined in two very different ways. The first is that of vibration through bone conduction. As vibrations pass through whichever medium the sound is moving through, the vibrations are interpreted by the individual. Some consider this a different form of hearing. For example, Beethoven composed some of his greatest works while he was deaf. How did he do this? Aside from being a master pianist, some critics believe that he put his ear against the piano, played something, and was able to “hear” based on the different types of vibration produced by the keys. Other examples are deaf dancers who dance on hollow, wooden boards, and are able to dance with the music based on feeling the vibrations of the song through their feet. This, of course, is not true hearing, but rather a physical interpretation of the vibrational energy produced by the musical notes being played.
So, what does a person who is completely deaf hear? Is there, indeed, a sound of silence that they are experiencing? The answer is yes and no. Once the auditory processing system of the brain goes without stimuli, whether it be through problems in the ear or problems in the synaptic receptors of the brain, the brain neurons go a bit haywire. When this happens, the brain begins generating its own activity resulting in a ringing, buzzing, or a humming sound called tinnitus. One woman named Sylvia, in Nina Raine’s Tribes, reports on the experience of going deaf, “No one told me it was going to be this noisy … It’s this buzz. This roar and outside … it’s all—black.”
For most, tinnitus is a very troubling experience. The buzz is constant and maddening. It often creates depression or anxiety within the person who must endure its drone, and can often interfere with daily life and concentration. Yet, if someone was born deaf, it is unlikely that they know the difference between having tinnitus or not. To them, the eternal hum is part of their daily life, and probably doesn’t affect them at all. If you’d like to experience the progression of becoming deaf, you can listen to a hearing loss simulator found on the Internet.
You can’t recreate the sensation of being deaf by plugging your ears, but you can experience the sound of silence in rooms specially designed to eliminate sound. These rooms are called anechoic chambers, and are so quiet that many people report having visual and auditory hallucinations while sitting in them.
Typically used to test products like audio equipment or aircraft fuselages, anechoic chambers are designed to absorb and eliminate sound. The rooms are so quiet that people report being able to hear their own heartbeat, blood rushing through their veins, or their stomach and digestive system working. Through a combination of architecture and special materials, anechoic chambers are made by strategically placing fiberglass acoustic wedges throughout the room set inside double walls of insulated steel and foot-thick concrete. The floors are usually made up of a mesh wiring, making the room so quiet that you can hear a pin drop. The rooms are said to be 99.99% sound absorbent, recording around 10-20 decibels (equivalent to the sound of calm breathing). Comparatively speaking, a quiet house is about 40dB(A), a whisper is about 30 dB(A), and listening to a busy freeway from fifty feet away is around 80 dB(A).
For awhile, the world’s quietest anechoic chamber was the Test Chamber at Orfield Laboratories. Scientists measured the interior of the room to be -9.4 dB(A) (decibels A-weighted). However, recently, Microsoft’s anechoic chamber measured at -20.6 dB(A). Most of the time, people can’t last more than 15 minutes in an anechoic chamber. Orfield Laboratory claims that the longest anyone lasted in their Test Chamber was 45 minutes. At that point, the person reported vivid auditory hallucinations, airing on the brink of madness. Some people report visual hallucinations as well, along with feelings of intense uneasiness—as if a demon or haunting spirit were lurking nearby.
In 2008, Radiolab co-host Jad Abumrad decided to sit in a completely dark anechoic in Bell Labs, New Jersey, for an hour. Abumrad reported hearing swarms of bees after having been in the chamber for only five minutes. His hallucinations continued. He said he heard other sounds such the wind blowing through trees and an ambulance siren. After 45 minutes of sitting in the chamber, he heard the Fleetwood Mac song, “Everywhere,” as if it were coming from a neighbor’s house. “The room was quiet, my head apparently is not,” Abumrad reported.
The Quietest Place on Earth
Jad Abumrad’s experiment and consequential realization are actually quite profound. Similar to the tinnitus, auditory hallucinations suggest that the brain demands some sort of sound-sensory experience. If deprived of auditory input, the brain will create sound, even if that sound is something similar to static. Trevor Cox, a professor of Acoustic Engineering at the University of Salford said, “For a long time it was assumed that sound simply enters the ear and goes up to the brain. Well, there’s actually more connections coming down from the brain to the ear than there are going back up to it.”
Given the right circumstances, the brain will produce its own experience of sound. Deprived of other senses, the brain recreates the world it knows. If the brain cannot distinguish between reality and hallucination, then the sound is a bit of both. This means that during sleep, even though the body is paralyzed and the brain is functioning on a theta wavelength (as opposed to a beta wavelength), it is actually possible to hear sound not generated or originating from the real world. In The Interpretation of Dreams, Freud writes about this experience of hearing sounds in our sleep. “We are all abnormal in the sense that there is no actual source of the sound around; all the voices are silently generated by our minds, not by some external entity” (Freud).
In another study, researches put volunteers into an MRI machine and asked them to watch 5-second, silent movie clips. The clips implied sound, but had none, such as a dog barking or a musical instrument being played. Although the clips were muted, several of the volunteers stated that they could “hear” the sound in their mind. The MRI scans supported their claim, noting that the auditory cortex centers of the brain were stimulated, even though the room was silent.
This suggests that the brain does not need auditory stimuli to experience sound. If the brain has any sort of recognized visual input, it will recreate the corresponding sound in the auditory cortex. This also suggests that when we hear sound, we are hearing not only the physical input of the sound waves, but are also simultaneously experiencing a psychological recreation of what that sound experience has been like in the past. That means that you only hear true sound the first time you experience it. Every time after, your brain is anticipating what it will hear and combining that internal past-experience with the actual external stimuli pushing its way into your ear.
The Sound of Silence
Based on this information and the aforementioned studies, it can be determined that silence does have a sound. Yet, this is only because sound is an experience interpreted by the brain. In space, there is no sound, yet even if one were to hold their breath and stop their pulse, they would still experience the internal hum of tinnitus. The brain demands stimuli, and if we deprive it of such, it will create its own.
So, the next time someone asks you, “If a tree falls in the forest with nobody around to hear it, does it make a sound,” you can respond, “It depends on who you’re asking.” A physicist would laugh at the question, because the crashing of the tree propagates audible waves of pressure, therefore making a sound. The physiologist or psychologist might pause for a moment, though. Their answer depends on equivocation, or the unique parameters defining sound. To them, sound might be the reception (rather than the expression) of vibrations perceived by the brain. They could argue that it depends on the perceiver of sound, whether or not the tree makes a sound while crashing in the woods. To them, no audience means no sound. Here, 18th-century philosopher George Berkeley might have a chuckle because his ideals of subjective idealism suggest that God is always present, therefore creating an omnipresent audience. This, however, is best saved for another article.
© 2018 JourneyHolm