How do we hear?

Why is Noise, Noise?

Our ears can distinguish between regular and irregular vibrations. When regular vibrations strike the ear, we recognize them as music or speech. On the other hand, if irregular vibrations strike the ear we may describe them as hissing, squeaking, rustling, creaking, rattling… what we often call background noise.

Why Are Loud Sounds, Loud?

Loudness is an impression we get about a sound’s strength through changes in pressure that we feel in our ears. The stronger the pressure, the louder we perceive the sound to be. When we talk about loudness, we use the term decibel (dB).

Sensitivity of the Ear

The range of normal human hearing is so sensitive we can detect the whisper of a dry leaf in the tree overhead (20 dB), yet so flexible we can tolerate the sound of a jet plane taking off (120 dB). At any age our hearing sensitivity can begin to change until we realize that it’s just not the same as it used to be. Sometimes soft sounds become too soft for us to hear, and loud sounds are too loud for us to tolerate.

Adaptation

Measurements have shown that when our ears are exposed to louder continuous sound, their sensitivity decreases. When the sound finally stops, our hearing sensitivity will slowly return. This phenomenon is called adaptation.

Fatigue

When subjected to loud sounds for long periods of time, our ears lose some sensitivity to sound. They become tired or fatigued. The longer the exposure to the sound, the longer it takes our ears to recover.

How does the ear work?

Outer Ear and Ear Canal

Sound vibrations travel through the air in waves to reach our ears. Large or small, these sound waves are first collected in the outer visible portion of the ear called the pinna and then funneled down through the ear canal to the eardrum.

Middle Ear

As the eardrum vibrates back and forth in time with the waves coming down the ear canal, it creates tiny corresponding motions that move along the three small bones of the middle ear collectively called the ossicles.

Middle Ear

As the eardrum vibrates back and forth in time with the waves coming down the ear canal, it creates tiny corresponding motions that move along the three small bones of the middle ear collectively called the ossicles.

Inner Ear or Cochlea

The third and smallest bone of the ossicles, the stapes, is embedded in the oval window of the inner ear, where its movements cause corresponding wave-like motions inside the cochlea’s fluid filled chambers. Each corresponding wave movement of the fluid causes tiny hair-like nerve cells to bend, sending electrical impulses along the auditory nerve to the communication centers of the brain.

These hair-like nerve cells (hair cells) are fragile and easily damaged. Loud sounds make big waves and cause the hair cells to bend so violently that they flatten or break. Once flattened, these hair cells may never regain their former shape or sensitivity to fluid movement in the inner ear. As more and more hair cells flatten, our hearing sensitivity reduces.