What is an audiogram?
An audiogram is a graph that shows the softest sounds a person can hear. Sounds are measured and recorded at varying pitches or frequencies. At least 6 frequencies are tested between 250Hz (low pitched) and 8000Hz (high pitched). One of the main reasons for this is that this 250-8000Hz range covers the frequencies of human speech production. On an audiogram, a red “O” symbol is used to represent air conduction responses for the right ear, a blue “X” symbol is used to represent air conduction responses for the left ear and a triangle symbol is used to represent the bone conduction result. Air conduction testing measures how an individual hears when the sound is presented via headphones. The sound has travelled through the whole of the auditory system; from the outer ear, through the middle ear and into the inner ear where it is transmitted to the brain via the nerve fibres. The bone conduction stimulates the inner ear directly. Sounds are transmitted via a transducer that is put directly onto the mastoid bone (the bone you can feel just behind your ear). This test can help to rule out any problems with the outer or middle ear.
The numbers on the vertical axis are measured in decibels and the numbers on the horizontal axis refer to the frequency that has been measured. The closer the marks are to the top of the graph, the softer the sounds that can be heard and therefore the better the hearing is. Any result between 0dBHL (decibel hearing level) and 20dBHL is classed as within normal limits. Here is an example of a complete audiogram, split onto two graphs (one for each ear).
This audiogram shows a moderate to severe high frequency hearing loss. This person has very good low frequency hearing, which becomes worse as the frequency increases. The hearing in the right ear is worse than in the left as it is further down the graph at many points.