Selective Hearing

Have you ever walked through a factory where the noise of rumbling machines filled the air, or an airport where planes constantly roared overhead? How could anyone work under these conditions without hurting their ears? It’s not just a problem in industry. Every day we repair our homes with noisy power tools and surround ourselves with blaring music.

Yet most of the time, we hardly notice. It’s all because the Creator gave our sense of hearing a built-in safety mechanism that defies natural explanation.

Your eardrum is wonderfully designed to sense the tiniest changes in air pressure. But this has a potential downside. Loud, sustained noises could easily push the delicate parts of the inner ear beyond their safety limit, causing permanent damage.

By God’s wise design, however, something special happens under these conditions. God put a series of three tiny bones in your middle ear to pick up most vibrations. For their protection, He attached two tiny muscles to the first and last of these bones (the malleus and the stapes). At the instant these bones begin to vibrate beyond normal limits, the brain senses danger and sends a signal to tighten the muscles and momentarily shut down the ear’s sensitivity. This happens in a split second and is involuntary, a phenomenon called negative feedback.

• Try this experiment yourself.

The inner ear is thus protected from injury. In an opposite situation, with very soft sounds, the muscles may loosen somewhat to increase sensitivity. This delicate balancing act allows us to hear a wide range of sounds without damage.

Where Did This Protection Come From?

How could this built-in safety mechanism possibly arise naturally by evolution if early humans rarely experienced loud sounds other than perhaps thunder or the roar of a nearby predator? Constant loud sounds and background noises are a modern phenomenon, with industrial machinery, blaring audio speakers, and gas-driven motors. Yet the ear of the original humans was already fully equipped to protect us before these threats even arose.

It is reasonable to suggest that the all-wise Creator planned ahead to protect our ears from modern industry’s noisy environments. In contrast, evolution cannot explain how random mutations could possibly plan ahead for future needs.

What Did You Say?

Our ears are tuned to hear a chorus of sounds each day, whether a croaking frog, the whistle of a train, the humming of a computer, or a beautiful singing voice. Imagine the range. Mariah Carey, one of the most versatile singers today, can hit five different octaves; a pianist can produce seven octaves; but our ordinary ears can detect ten!

A few animals, such as bats and whales, can hear higher pitches. (They rely on sonar to navigate because the signal doesn’t deteriorate very quickly.) Elephants, on the other hand, hear lower pitches. (Why? So they can share information in a pitch other animals can’t overhear!) But our range is quite impressive and meets all our needs.

Sound is actually a vibration, like plucked violin strings that jostle air molecules. These invisible molecules then transmit the vibration through the air as minor pressure changes. Our ears can sense vibration frequencies between 20 and 20,000 cycles per second (hertz). High-pitched tones cause the ear to vibrate 20,000 times each second, or more than one million times in 50 seconds, without bursting.

The greatest danger to your ears is not high or low pitches but intense sounds (measured in decibels). Your ear must be prepared at all times to hear any intensity, from a mouse creeping behind your desk (nearly 0 decibels) to a jet engine (over 160 decibels). Your job is to take precautions or cover your ears. But God has given you help through the feedback mechanism.

How appropriate that King David honored his Maker in Psalm 139:14, “I will praise You, for I am fearfully and wonderfully made; marvelous are Your works, and that my soul knows very well.” Hearing is a special gift from the Creator, who hears and sees everything: “He who planted the ear, shall He not hear? He who formed the eye, shall He not see?” (Psalm 94:9).

See for Yourself . . .

Sound waves do not travel underwater or along a string in the same way they travel through the air. You can test the difference with a simple experiment using a string and a kitchen fork. You can make the sound of a vibrating fork seem like a large, melodic church bell!

Materials

• Three feet of string
• A metal fork and spoon

Procedure

Tie a small loop at one end of the string.

Now pull the free end of the string most of the way through this loop. This results in a larger, adjustable loop, which you can temporarily attach to the fork.

Place this loop around the handle of the fork and pull the string tight. You may need to add a bit of tape to prevent the fork from slipping free.

Dangle the fork at the end of the string and tap it with the spoon. A weak metallic sound will come from the fork.

Now wrap the free end of the string around your finger several times.

Hold the finger gently against your ear canal so that it closes the opening, with the fork suspended freely below.

Once again, gently tap the spoon against the fork. How does the sound compare this time? The deep, pleasant ringing may remind you of a church bell.

The Lesson

After it is tapped by the spoon, the fork vibrates for a second or longer. When these sound waves move through the air, they die away quickly. The string, however, carries the vibrations directly through the bones in your skull to your inner ear, without their being lost in space. As a result, you hear a richer sound.

The bell-like sound is mainly due to lower frequency vibrations (lower pitch), which the string carries directly through your bones to your inner ear. For further study, try different sizes of metal forks. A smaller size should vibrate more rapidly, giving a somewhat higher-pitched sound.