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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?)
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