TESTS AND AUDIOGRAMS
Hearing tests are designed to find
out what you can and can’t hear, and audiologists
are skilled at using a range of techniques to find
out what your hearing is like. The following information
explains what the most common of these tests are about
and what the results mean.
How is hearing tested?
The most simple test of hearing
ability is called 'pure tone audiometry' where you
listen to a range of beeps and whistles (called pure
tones) and indicate when you can hear them, maybe
by pressing a button. The loudness of each tone is
reduced until you can just hear the tone. The softest
sounds you can hear (your hearing thresholds) are
then marked on a graph called an audiogram.
When hearing is measured with pure
tones presented through headphones, this measurement
is called air conduction. The sounds go via the air,
down the ear canal, through the middle ear, and to
the very delicate organ of hearing in the inner ear—the
The sensitivity of the cochlea can
also be tested by placing a small vibrator on the
mastoid bone behind the ear and again measuring the
softest sounds that can be heard.
Sounds presented this way travel
through the bones of the skull to the cochlea and
hearing nerves, bypassing the middle ear. This type
of testing is called bone conduction.
The air conduction and bone conduction
hearing levels on the audiogram can tell us a lot
about where the hearing problem is.
What exactly is an audiogram?
Look at the blank audiogram graph
Along the top of the graph the
numbers range from 125 to 8000. These numbers refer
to frequencies, or different pitches of sounds.
Frequency is expressed in terms
of the number of cycles per second, or Hertz. The
higher the number, the higher the pitch of the sound.
For example, 250 Hertz (250 Hz) sounds like middle
C on the piano, while the high-pitched ringing of
the telephone is about 3000 Hz.
Normal, young, healthy human ears
can actually hear frequencies as low as 20 Hz and
as high as 20,000 Hz, but we only test hearing in
the range of 250 Hz to 8000 Hz, as most sounds of
speech occur in this frequency range.
Loudness or level of sounds is measured
in units called decibels. Zero decibels (0 dB) does
not mean ‘no sound’. It is just extremely
soft. Conversational voice level is around 65 db,
and 120 db is very, very loud—about as loud
as a jet taking off when you are standing 25 meters
away. The figures along the side of the graph are
hearing levels in decibels.
Air conduction thresholds for the
right ear (that is, the softest sounds the right ear
can hear at each frequency) are marked as an ‘O’,
and the left ear is an ‘X’ on the audiogram.
Bone conduction thresholds are marked on the audiogram
as ? (better ear), [(right ear) or] (left ear).
What does the audiogram mean?
Your audiogram is a ‘picture’
of your hearing. It indicates how much your hearing
varies from normal and, if there is a hearing loss,
where the problem might be located in the hearing
If the hearing thresholds obtained
by bone conduction are the same as the air thresholds,
this indicates no blockage of sound in the outer or
middle ear. We could safely assume the hearing loss
is caused by a loss of sensitivity in the cochlea
or hearing nerve. This type of loss is called sensorineural
(pronounced sen-sorry-new-rol) hearing loss.
An Example of a mild to
severe sensorineural hearing loss in both ears.
Many things can damage the delicate
hearing nerves. Exposure to excessive noise can cause
a sensorineural hearing loss, and so can the ageing
process. There is rarely any medical treatment for
sensorineural hearing losses and so the impairment
If the bone conduction hearing thresholds
are normal, but there is a loss of hearing for air-conducted
sounds, this is called a conductive hearing loss.
This means that the cochlea is normal and healthy,
but there is some blockage to sound in the middle
or outer ears.
Middle ear infection is a common
cause of a conductive hearing loss in young children.
Outer and middle ear blockages can often be corrected
by medical or surgical treatment.
An Example of a mild cunductive
hearing loss in both ears.
It is possible to have both a sensorineural
and a conductive hearing loss (e.g. if a person has
a noise caused impairment and a perforated ear drum).
This is called a mixed hearing loss.
An Example of a moderate
to profound mixed hearing loss.
This is not a hearing test, but
a test of how well the middle ear system is functioning
and how well the eardrum can move.
A small rubber tip is placed in
the ear and a little air is pumped into the outer
ear canal. If there is a problem in the middle ear
it may show up on this test. For example, if there
is very little movement of the eardrum, it may indicate
fluid behind the drum as a result of a middle ear
Often the results of tympanometry
indicate the location of the blockage that is causing
the hearing loss and if medical treatment may help.
Speech perception testing
The ability to hear speech is a
function of 2 abilities.
- The ability to detect the sounds of speech.
- The ability to understand speech.
The audiogram shows how much sound
someone can detect, but does not tell us how clearly
speech can be heard by the hearing impaired person.
Predictions can be made from the degree and type of
hearing loss, but to measure a person’s speech
discrimination—how well they can understand
speech—special tests are used. For example,
words may be presented (usually at different levels
of loudness) which the hearing impaired person has
A person who has a problem understanding
the words, even when they are loud enough, may find
the benefit provided by a hearing aid will be limited.
People who have a sensorineural hearing loss often
fall into this category. Generally speaking, the greater
the hearing loss, the poorer the speech discrimination.