Look at the blank audiogram graph below. 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 (250Hz) sounds like middle C on the piano, while the high pitched ringing of the telephone is about 3000Hz.
Normal young, healthy human ears can actually hear frequencies as low as 20Hz and as high as 20,000Hz. However, we test hearing in the range 250Hz to 8000Hz, as most of the sounds of speech occur in this frequency range.
Loudness or level of sound is measured in units called decibels. Zero decibels (0dB) does not mean “no sound” – it is just extremely soft. Conversational voice level is around 65 decibels, and 120 decibels (120dB) is very, very loud – about as loud as a jet taking off if you are standing 25 metres away! The figures along the side of the graph are hearing levels in decibels. Air conduction hearing thresholds for the right ear (ie. The softest sounds the right ear can hear at each frequency) are marked as an “O” and the left hearing thresholds are marked as an “X” on the audiogram.
Bone conduction thresholds are marked on the audiogram as P (better ear), [(right ear) or] (left ear).
The audiogram gives a “picture” of your hearing. It indicates how much hearing varies from normal and, if there is a hearing loss, where the problem might be located in the hearing pathway.
If the hearing thresholds obtained by bone conduction are the same as the air conduction thresholds, this indicates that there is nothing stopping the sound from traveling through the outer or middle ear to the cochlea.
If the bone conduction hearing thresholds are normal, but there is a loss of hearing for air conduction sounds, this is called a conductive hearing loss. This means that the cochlea is normal, but there is some blockage to sound in the middle or outer ears.
Middle ear infections, called Otitis Media, can cause a conductive hearing loss. Middle ear conditions caused by Otitis Media can be corrected by medical or surgical treatment.
It is possible to have both a sensorineural and a conductive hearing loss. For example, if a person has impairment due to noise exposure and a perforated ear drum. This is called a mixed hearing loss.
More information:
Information provided by Hearing Australia. Reproduced with permission.
Disclaimer: The information contained on this website is not intended as a substitute for independent professional advice.
