Hearing can be measured in different
ways.
It can be done by testing how well someone
understands speech either at normal voice levels or whispered.
However, there are two key problems with this type of testing.
First, it is difficult to maintain constant intensities of
speech and second, because speech is made up of many sounds that
differ widely in frequency or pitch, a hearing loss that is mainly
confined to a particular frequency region may be missed. So most
audiologists measure hearing by using test techniques that provide
sounds of known intensity and specific frequencies.
To ascertain the type of hearing loss, hearing
is measured using earphones (which measure air conduction) and by
placing a small vibrator on your head (which largely bypasses
the eardrum and middle ear and measures the sound waves that pass
directly to the cochlea in the inner ear) and this measures the
overall efficiency of your hearing.
With the earphones, the listener is provided with tones of
different frequencies, testing one ear at a time. The intensity of
each tone is varied to find the lowest level that the listener can
hear, which is then described as the threshold for that tone.
It is unusual for someone's hearing threshold to be the same or
similar for different frequencies - usually there is a greater
hearing loss for high frequency tones. Equally, hearing loss can be
different in each ear. We measure hearing loss in units called
decibels hearing level (dB HL for short).
Also see: What happens during
the hearing test?
After your hearing test, your hearing aid
audiologist will plot the results on a graph and use the
measurements to tell you the extent - if any - of your hearing
loss.
Mild hearing loss
20-40 dB HL You cannot hear soft sounds and
you struggle to understand speech in noisy places.
Moderate hearing loss
41-70 db HL You cannot hear moderate
sounds and have difficulty understanding speech when
there is background noise.
Severe hearing loss
71-95 db HL You have to ask people to raise
their voices and group conversations are extremely
difficult.
Profound hearing loss
More than 95db HL You can only hear some very
loud sounds and communication is impossible without hearing
aids.
