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How Hearing Works

Hearing and understanding speech is an essential component of human communication.
To achieve this, the ear functions as a high-performance instrument:

  • It can perceive sound ranging from very soft to painfully loud, and in doing so it processes sound pressurelevels with a physical variation factor of about 100,000,000!
  • The range of frequencies which the ear can perceive is between 20 and 20,000 Hz.
  • Thanks to its directional hearing capacity the ear can localize an acoustic source to within an accuracy of 2°.

In order to achieve these remarkable feats, each part of the ear - outer, middle and inner ear -
fulfils a particular function.

Outer ear

The funnel-shaped external, or outer ear, collects the sound waves and transmits them to the external auditory canal. The shape of the flap of the ear is important for directional hearing.

The external auditory canal is approximately 2.5cm to 3.8cm, ending at the eardrum.

The shape of the external auditory canal acts to increase the volume of frequencies important
to understand speech.

Middle ear

The sound waves in the external auditory canal cause the eardrum to vibrate.

The ear bones, or ossicles, (called hammer, anvil and stirrup because of their characteristic shapes) amplify the movements of the eardrum and transmit them to a small membrane in the inner ear.

The positioning of the three ear bones is important. It ensures that the sound waves are transmitted to the inner ear with as little loss of signal as possible.

Small muscles on the bones protect the inner ear from too much noise by restricting the ability of the ear bones to move when the sound is very loud.

The Eustachian tube, a connection between the middle ear and the pharynx, ensures that watery secretions can drain away and that the middle ear is ventilated.

Inner ear

The inner ear consists of two main parts: the semicircular canals, which are important for our
sense of balance, and the cochlea.

The interior of the cochlea is filled with a fluid (lymph) in which the sound expands in the form of a pressure wave.

This pressure wave stimulates thousands of acoustic hair cells.

These hair cells convert the mechanical sound signal into an electrical stimuli.

These electric stimuli are transmitted to the brain via the auditory nerve.

In the brain these stimuli are processed and we perceive them as sounds.

 


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