What can Affect Hearing Process

I will explain here a hearing process and what can affect it.

Sound waves come through ear canal, reach eardrum and swing it. Vibrations are carried via three hearing bones (in the middle ear) toward the cohlea and causes the liquid within to oscillate. This stimulates hearing receptors. At this point mechanical vibration is converted in nerve excitation which propagates via auditory nerve through brainstem and reaches the brain. Excitation of brain cells in auditory area is recognised by a person as a sond.

**At all this points a sound can be impaired by objective and subjective causes**.

Objective causes:
A foreign body, injury, infection... in ear canal.

Any procees which press on auditory nerve on his path toward the brain.
Changes within the auditory nerve.
Vascular (aneurysm) or blood disturbance (thrombosis, policythemia).

Subjective causes:
Psychic tension, Pain...
Tension can cause the muscles in the middle ear to contract, which can objectively affect the perception of loudness.

All these causes can not only prevent hearing but can also distort a sound or can pruduce tinnitus.

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Sound related Terms

The Sound is a propagation of vibration (with 20-20,000 Hz frequency) through the medium (air, liquid solid matters). It is a mechanical force which causes vibration of the tympanic membrane (eardrum).

Loudness of a sound is determined by pressure of sound waves puts on an eardrum. Measure unit is decibel (dB).
Hearing threshold is at 0 dB.
Normal Talking at 1m distance ...40-60 dB.
Major Road at 10m distance... 80-90 dB.
Prolonged exposion to 85 dB can cause hearing imparmient.
Short exposion to 120 dB can cause hearing damage.
Plane on the airport...120-140 dB.
Treshold of Pain...135 dB.

Hight of the sound is determined by frequency of sound waves.
High frequency means high sound.
The hearing range is between 20Hz to 20,000 Hz and it changes with age. Old people usually can't hear sounds over 16,000 Hz.
Sound out of this frequency range cannot be heard. Sound over 20,000 Hz is called Ultrasound, below 20 Hz is Infrasound.

Tone is a sound of a particular frequency. 'Middle C' has 262 Hz, 'high C' has 512 Hz.
Monophonic sound is composed from one tone
Polyphonic sound is composed from two or more tones.
Hiss is a sharp sibiliant sound like sustained 's'.
Noise can be defined as unwanted sound.
Resonance is a relatively high amplitude of vibration produced when a frequency of some source matches the natural frequency of other object.

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