How do we hear?
Although very complex here is a simplified version.
The ear although very handy for hanging glasses or earrings
does a very specific task. The pinna acts like a funnel
to collect and direct sound vibrations down the ear canal
to the eardrum. Whilst doing this the vibrations that
are the most important are slightly increased.
The canal also protects the eardrum from damage. Sound
vibrations reach the eardrum causing it to vibrate.
Sound is now changed to mechanical energy, at the back
of the drumhead there are tiny bones (the smallest in
the body! the malleus, incus and stapes) that move with
a lever motion.
The energy passes through these bones and reaches the
cochlear. This is a small cavity which resembles the shell
of a snail. Inside there are tiny hairs (cillia) and fluid.
Once inside the energy causes a vibration within the
fluid and it is this movement that causes the hair cells
to move. When the hair cells move they trigger an electrical
impulse to the brain.
Which hair cells have been stimulated depends upon the
frequency of the sound. The first turn of the cochlear
is responsible for high frequency sounds, the mid turn
for the mid frequencies and the last turn (apex) for the
low (Bass) frequencies.
The electrical impulse travels along the auditory nerve
to the brain, which interprets the impulses.
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2 Ears are better than 1!
Who can benefit from a stereo hearing system?
Scientific research as well as individual experience
confirms that most people with a hearing loss in both
ears would benefit from having two hearing instruments,
even if the hearing loss is mild. There are a few isolated
cases where this is not so - your hearing care professional
or physician can advise you.
Sound localization
The ability to localize sound is dependent
on two properly functioning ears. How do we know the direction
of a car's approach? The sound reaches the closer ear
a few micro-seconds earlier, and with a somewhat greater
intensity, than it reaches the other ear. These minute
differences in the signal transferred from the ear to
the brain enable us to make important, potentially life-saving
decisions regarding the exact location of the car. When
one ear functions better than the other, there is inadequate
information to quickly and reliably determine the origin
of a sound.
Understanding speech in a noisy
environment
Hearing with two ears provides improved
capacity to suppress background noise, making it easier
to understand conversation.
Unequal hearing in the left and right
ears is a big disadvantage in noise. While one hearing
instrument may be helpful in noisy situations. The greatest
difficulty understanding speech occurs when several people
are talking at once. This is common during interactions
between family, friends and colleagues at work. Often
these exchanges are also taking place in noisy surroundings.
With two hearing instruments it is possible to maximize
understanding in noise.
Hearing with less volume
A sound presented to both ears is judged
to be louder than the same sound, at the same intensity,
presented to only one ear. This means that a user of two
hearing instruments can set the volume of each one lower,
resulting in more pleasant hearing and less amplification
of distracting background noises.
Hearing equally from both sides
Wearing two hearing instruments gives
the maximum opportunity to respond accurately and confidently,
whether the conversation comes from the left or right.
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Hearing
Thresholds
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