- our brain analyzes the pattern of sound waves picked up by our ears, so that we can know whether we have heard a foghorn or a bird call.
- our hearing equipment is so sensitive that our nerves respond to vibrations of the ear membrane no greater than 0.0000001 millimeter in width!
- we identify sounds by their volume, pitch and tone.
- all sound has pitch and volume.
- the human ear is sensitive to frequencies between 20 and 20,000 Hertz (between 20 and 20,000 vibrations per second). The higher the frequency, the higher the pitch of the sound.
- a dog is able to hear higher pitches than our ears can register—in the range of 30,000 Hertz.
- bats are able to produce and hear sounds of approximately 100,000 Hertz.
A Few Definitions:
- Pitch is related to the frequency of the sound wave, i.e., how many vibrations per unit of time. Each vibration is one-cycle (one wave, one back-and-forth). The units of frequency are called Hertz (Hz). One Hz is equal to one vibration per second.
- Volume depends on the intensity of the sound wave (how deep or “high” the sound wave).
Our world today is full of noise—screeching sirens, blaring radios, rushing traffic, roaring jets—sometimes we almost wish we could not hear. But only almost, for hearing also brings us the singing of birds, the rustle of wind in the trees, the deep breathing of a child, the majesty of music, the loving voice of a friend, the warning of danger. There is just no substitute for hearing. Thank God, we can hear!
Yet hearing is one of the most delicate functions of the body. After many centuries of study, the most brilliant minds still admit that they do not fully understand the intricate process by which we hear. And shall we think that the delicate mechanisms in our body that transmit and interpret sound came about by chance? What human engineer could compress into one cubic inch a complete sound system, including an amplifier, an equalizer, a transducer, a power supply, and all the other equipment necessary to receive and relay sound? And even if an engineer could perform this feat of miniaturization, he could not hope to approach the ears' performance.
Even looking briefly at the mechanisms by which we hear should increase our gratitude to the God we serve, and our deep longing to please Him who has provided so bountifully for His human family. If He has done so much for His earthly creation, what of the wonders He is holding in store for every loving, faithful, obedient child?
What Is Sound?
Two centuries ago the question set debates raging among the intellectuals of Europe. “If a tree falls in the forest,” said the eighteenth century thinker, “and no one is there to hear it, will there be a sound?”
“Of course,” said the physicists, who were then struggling to measure and analyze everything around them. ”Sound is the result of vibrating air molecules, and the air vibrates whether or not any human ears are present to interpret them.“
“Of course not,” said the philosophers, who were questioning all nature in search for the “real” world. “Sound is a sensation known only in the mind of the listener.”
Actually, both were right. Sound originates when a body moves back and forth rapidly enough to send waves through the medium in which it is vibrating (usually the air). But before the sound can be “heard,” the sound waves must be received by the ear and changed into electrical impulses which can be interpreted by the brain.
Sound is the result of molecules—whether in the form of a solid, liquid, or gas—in motion. In 1663, a British scientist named Robert Boyle suspended “a watch with a good alarum” from a slender thread in a glass jar, then pumped the air out of the jar. “We silently expected the time when the alarum should begin to ring… and were satisfied that we heard the watch not at all.
Wherefore ordering some air to be let in, we did… begin to hear the alarum.” Boyle had demonstrated that sound does not exist unless there is a substance through which its vibrations can be transmitted.
Any vibrating object (a taut string, a solid plate, or a column of air) can be a source of sound. Let a drummer crash a loud cymbal. The vibrating plate sets the surrounding air molecules in motion (in waves), much as when you drop a pebble into a pond of water. The waves travel in all directions. Our ears pick up the vibrations, concentrate them in a small area, amplify them, then change the vibrations to electrical impulses which our brains interpret, and—we hear!
Our ears are designed to be very, very, very sensitive to vibration. A normal young person's ear is able to detect sound for which the motion of the air molecules is less than one 10 millionth of one percent—this represents a particle displacement of less than the diameter of one atom (100 million atoms set edge to edge equal the thickness of a single sheet of paper).
Even a very loud noise causes only microscopic movements of our eardrum. A high frequency sound may move the membrane no more than 0.0000001 millimeter—and we hear it!
How is it possible? How can we hear a whisper—or a mosquito flying by? because the force pushing on our eardrum is increased as many as 180 times as it travels some two inches through our ear system.
Yet the amplification process is selective. conversation (a range of 3,000 to 5,000 Hertz) receives the greatest boost (by chance?); and our equipment is too stiff to respond at all to the very lowest tones. Do we wonder why? If the range were not limited in this way, we would be assailed constantly by the sounds of our own body—our muscles contracting, food digesting, blood gushing through our veins, our bones creaking as we move—and how would we ever be able to think or concentrate! (Did such a limitation—on a marvelous amplifier system—come about by chance?)
Ears By Two's
Our Creator has given us two ears. Did we ever wonder why? If we were to try hearing for a while with just one ear, we would quickly know.
First of all, two ears give us a pleasing and understandable reception of many sounds—having an ear on each side of our head means that we actually hear in stereo!
Second, two ears are useful in maintaining a sense of balance—the fluid in our inner ears tells us what is “level” and what is not.
Two ears are also useful in identifying a source of sound.
Distinguishing Sounds
From the time we are born we are receiving an uninterrupted stream of sounds from the outside world, which we screen, sort, and file away. A normal adult has stored in the brain some 400,000 different signals, for future reference. Here is a recording and retrieval system worth noting—at the very least, we should give credit to the Designer!
But when—if ever—do we hear only one sound at a time? Go outdoors, and see how many sounds you hear—simultaneously. If we analyze them, we realize that each is different. How does our ear process and sort all these different wave forms at the same time?
Our ears can actually hear some sounds and reject others. No one really understands how, but from a confused and unorganized maze of signals we are able to hear what we really want to hear. We can shut out a volume of background noises—even very loud noises—to distinguish a familiar voice. A conductor can screen out the sound of many instruments to hear a particular line of music. A mother can identify the cry of her own infant in a nursery where many children are crying. How is it possible? We can only thank our marvelous Creator!
Even while we sleep, our ears sort and select with incredible efficiency. Because the brain can interpret—even independent of our conscious mind—we may sleep soundly through train whistles and screeching traffic, yet awake promptly to the gentle voice of someone beside us—which tells us that our ears receive as well as send messages to the brain.
What is the process? Actually, there are thought to be dual sets of nerve fibers which serve as transmission lines between our two ears and the brain. Auditory signals from each ear travel to both sides of the brain, so that a dysfunction in one path will not significantly affect hearing in either ear. Who can think that such a system came about without intelligent design?
How We Hear
We can appreciate our Creator's gift to us even more if we look closer at the three different parts of our ear: external, middle and inner.
The External Ear
The external ear is basically very simple. It consists of a sound collector (what we call our “ear”), and a short canal which funnels the sound waves down to the eardrum. The canal leading to the eardrum is lined with tiny hairs projecting outward, which are covered with droplets of sticky wax—an effective device for snagging tiny insects or dust particles that might stray in. (Did “ chance” design such a simple protection?)
The eardrum is surely no chance mechanism. A thin, semitransparent partition stretched across a round opening in the skull, it is made up of three layers: the outer layer (skin), under which is a mucous membrane lining, inside of which is a layer of circular and radial fibers that give the drum rigidity and tension. It is also well supplied with blood vessels and nerve fibers that make it acutely sensitive to pain. The eardrum covers the entrance to the middle ear, and is designed to accurately transmit sound waves to the inner ear.
The Middle Ear
The middle ear is a small, air filled cavity in the bone. It is separated from the external ear by the eardrum, and from the inner ear by a thin bony partition which contains two small membrane-covered openings: the oval window and the round window. The middle ear also contains a tiny tube (the Eustachian tube), just over an inch long, that opens into the throat. This tube is very important in equalizing air pressure in the ear. If pressure on either side of the eardrum were not equal, the eardrum would not be free to vibrate at the correct rate, and we would not know what we were hearing! The tube to the throat is normally closed, but opens when we swallow, or yawn, allowing air from the throat to enter and leave the middle ear, making the inside and outside pressures equal. The tube is also lined with small, movable hair projections facing downward, which help to speed the drainage of secretions from the middle ear into the throat. (Did such a device come about by happenstance?)
Carrying sound waves across the middle ear and amplifying the sounds are three tiny bones, interlinked, commonly known (because of their shape) as the hammer, anvil, and stirrup. Here again is an intricate structure, for which we must thank our great Designer.
The first tiny bone, called the “hammer,” picks up the vibration of the eardrum, to which it is attached, and relays it to the next tiny bone, the “anvil,” which in turn transmits the vibration to the third bone, the “stirrup.” The stirrup (about one tenth of an inch in height) is attached to a membrane that stretches across the oval window of the inner ear; thus the vibrating pattern is transferred directly to the inner ear.
The middle ear also contains another wonder—two minute muscles anchored to the bone of the skull, which work together as a safety device. One muscle passes over a pulley-like projection and attaches to the upper part of the handle of the mallet, and one attaches to the neck of the stirrup. When a loud noise is heard, the first muscle pulls on the eardrum, restricting its ability to vibrate so that it will not be harmed by the loud noise; while the other muscle pulls the stirrup away from the inner ear membrane so that the inner ear fluids will not over-react. (What scheme of chance built a mechanism so delicate?)
The Inner Ear
The inner ear is where hearing really gets complicated. We can only touch on a few high points, but it should be enough to increase our gratitude to our Creator for designing such a high tech hearing mechanism—that really works!
First, the inner ear is heavily protected—it is located in a cavity in the hard bone of the skull, deep behind the eye socket, so that its intricate operations are well protected.
Inside the bone cavity is a delicate bone structure called the bony labyrinth, which consists of two main parts: a set of semicircular canals, which control our sense of balance; and a spiral-coiled cochlea (pronounced ko-KLE-a), which is the real center of hearing.
The cochlea is a pea-sized tube consisting of two and one half spiral turns around a hollow central pillar (its name was derived from the Greek word for "snail"). Winding with the spiral are three fluid-filled canals and a gelatinous membrane, through the center of which runs the most vital organ of hearing: the organ of Corti (named after the scientist who discovered this organ).
How does sound travel through the inner ear? Sound vibrations received from the middle ear move the membrane that stretches across the oval window—which moves the fluid in the canals of the cochlea—which moves the membrane that lies between these canals—which moves special hair cells that are attached to the membrane. In each ear are approximately 12,000 of these hair cells, and projecting from each hair cell are approximately 100 hairs. As the hair cell vibrates, these hairs move, creating an electrical stimulus. These hairs are connected to some 30,000 nerve fibers, which dispatch the messages to the brain—and we hear! (Aren't we thankful that we do not have to understand the process before we can hear?)
But none of the hairs have an exclusive right to a nerve transmitter. All the nerve fibers are “party lines”—over a million hairs must share a mere 30,000 nerve fibers. But this limitation does not seem to slow down the process of hearing— someone has calculated that our ears pick up as many as 100,000 signals a second!
A cross section of the organ of Corti is striking in its detail, especially when we consider how minute this organ is, and how critical in the process of hearing. (The entire organ is only about l.4 inches if uncoiled.) Is it not a miracle of design?)
How can we distinguish between low sounds and high? It seems that the cochlea is a “tuned” structure, i.e., different areas register different frequencies; but the process is by no means fully understood.
Sources:
- S. V. Letcher in Compton's Interactive Encyclopedia, copyright 1993 by Compton's NewMedia, Inc.
- Dr. A. J. Duvall, III and P. A. Santi in The 1995 Grolier Multimedia Encyclopedia
- The Incredible Machine, published by National Geographic Society, Washington, DC, copyright 1986
- Sound and Hearing, published by Time, Inc., 1965
- Principles of Anatomy and Physiology, copyright 1993 by Biological Sciences Textbooks, Inc., a division of Harper Collins New York, NY
- and the Encyclopaedia Britannica, 15th Edition, 25:204f
