How the Ear Works

How do we hear?

Sound is a vibration in the air that travels down the ear canal to the eardrum.  Behind the eardrum is the middle ear, an air filled space which contains three tiny

bones called the ossicles. Vibrations travel across the eardrum and along the ossicles to the inner ear which contains the hearing organ (the cochlea) and the balance organs. The cochlea looks like a small snail’s shell, about the size of the nail on your little finger. The cochlea is filled with fluid and contains thousands of tiny hair cells which act like electrical switches. Sound vibrations make waves in the fluid in the cochlea. These waves trigger the hair cells to send electrical signals along the auditory nerve to the brain where the sound can be interpreted.

 

Measuring hearing levels: the audiogram

A pure-tone audiogram is a graph used to record the quietest level of sound someone can hear. The pitch (or frequency, in Hertz [Hz]) of sound is shown across the audiogram and, like a piano, goes from low pitches on the left-hand side through to high pitches on the right. The level of sound is measured in decibels (dB HL) and gets louder going down the graph. Speech sounds are shown on the diagram at their pitch and sound level for normal conversational speech.

When we test the hearing, we try to measure air conduction and bone conduction levels to let us know the degree and the type of hearing loss.  Air conduction levels are measured from passing sound through the whole ear structure, including the middle ear and cochlea. Sounds can be played through loudspeakers, headphones or insert earphones.  Bone conduction levels are tested by playing sounds through a small vibrator that sits behind the ear and tests how sound is picked up by the cochlea, bypassing the middle ear (which can be affected by glue ear or other blockages).

When the levels are very similar for air conduction and bone conduction, this is called a sensorineural hearing loss.  When the levels are better for the bone conduction than the air conduction, this is called a conductive hearing loss.



Key

X Left air conduction

O Right air conduction

S Hearing when tested from a speaker. This tests both ears working together.

∆ Not-masked bone conduction.  This tells us about the best hearing cochlea.

] Left bone conduction

[ Right bone conduction

Last Reviewed: 28/03/2012