 How We Hear
How the Ear Works
Hearing Loss
How We Hear
Sources of Sound
When we "hear" sound, our ears are picking up air movement from either a vibrating object (like a violin string) or a rushing stream of air (like a flute or human voice). Sounds are able to reach our ears because it travels along a medium that "carries" vibrations. The medium that we are most familiar with is air. Sound vibrations can also travel through other mediums as well, such as water or steel.
Why is Noise, Noise?
Noise is an unwanted sound that creates a disturbance in the frequency range of interest. For example, if you are engaged in conversation (your frequency range of interest) and a train whistle blows, the whistle interferes with your conversation and is therefore considered noise.
One of the most common disturbances for hearing instrument users is the presence of background noise in restaurants, cars, and in the workplace.
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 a tree overhead (20 dB), yet so flexible that we can tolerate the sound of a jet plane taking off (80 dB). At any age and for many different reasons our hearing sensitivity can begin to change, making communication increasingly difficult. Sounds in the environment, especially speech sounds that were once perceived as loud enough to hear easily, may no longer be perceived as sufficiently loud to allow for easy communication.
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How the Ear Works
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.
Inner Ear or Cochlea
The third and smallest bone of the ossicles, the stapes, is embedded in a membrane, called the oval window, which separates the middle ear from the inner ear or cochlea. The cochlea is a fluid-filled chamber containing thousands of hair-like nerve cells. The movement of the stapes at the oval window produces corresponding wave-like motions of the fluid in the cochlea. Each corresponding movement of the fluid causes the hair cells to bend, sending electrical impulses to the auditory nerve and on to the communication centers of the brain.
These hair cells are fragile and easily damaged. Once they are damaged, the hair cells will not fully recover, resulting in reduced sensitivity and hearing loss. As more and more hair cells are damaged, the hearing loss becomes more severe. Hearing loss resulting from hair-cell damage is known as sensory or "nerve" loss and is generally permanent.
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Hearing Loss
Did you know that over 28 million Americans - men, women, and children
- currently suffer from hearing impairment? For most of the hearing
impaired, the use of hearing instruments could translate into improved
communication with loved ones and renewed enjoyment of life.
There are many reasons for hearing loss that can rob us of our ability to hear and understand the way we used to, such as:
Natural effects of aging
While aging does not always result in significant hearing loss, it is among the most common reasons. Hearing loss due to aging produces a permanent sensory loss.
Noise exposure
Exposure to loud sounds for prolonged periods of time can result in hair cell damage and permanent sensory hearing loss. Short extreme noise exposures can also produce permanent hearing loss known as acoustic trauma. Signs that damage has occurred to the hair cells following noise exposure is often evidenced by ringing in the ears called tinnitus. The tinnitus may subside after a short period of time but the effect of the noise exposure on the hair cells remains.
Illness
Some illnesses can result in damage to the hair cells. This is sometimes true of illnesses that produce high prolonged fever or those that require treatment with "ototoxic" medications. Ototoxic refers to medications that have the potential for damaging inner ear hair cells.
Birth defects
This results from events that occur that interfere with the normal development or functioning of the organs of hearing. Hearing loss of this type can be either sensory (hair cell or cochlea damage) or conductive, related to structures of the outer or middle ear.
Middle ear disorders
This refers to hearing loss that results from a medically related condition of the outer or middle ear. These can include infections, middle ear fluid, damage to the middle ear ossicles or an excessive wax formation that blocks the complete ear canal. This type of hearing loss is called conductive because it diminishes sound as it is conducted along the outer and middle ear on its way to the cochlea.
When hearing loss is suspected, an appointment with a hearing healthcare professional is recommended for the purpose of testing and evaluation. The majority of people who receive proper and regular professional care are successful hearing instrument users.
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