An audiogram is a chart of a persons hearing ability. There are some different styles of audiograms, but most use a standard set of symbols for representing items on the chart. It is always a good idea to review the key that accompanys each audiogram to verify that it uses symbols you are familiar with.
I have included some sample audiograms so that you may become comfortable with the terms and the symbols.
The audiogram reads in frequency (pitch) across the top or horizontal axis and it reads in decibels (loudness) down the side or vertical axis. Just like a piano's keyboard, the pitches are low on the left side (125 or 250Hz), and then gradually climb to higher pitches on the right side (8000Hz). The loudness scale goes from very soft sounds at the top (-10 or 0dB) to very loud sounds at the bottom (110 dB). It is important to remember that 0 dB does not mean that there is no sound at all. It is simply the softest sound that a person with normal hearing ability would be able to detect at least 50% of the time. Normal conversational speech is about 45 dB.
The softest sounds a person hears at each pitch at least 50% of the time are considered their hearing threshold. Thresholds are obtained and marked for most of the pitches across the audiogram. Typically, when testing is done with headphones, we call them "air" thresholds as the sound must travel through the air of the ear canal to be heard. An O is used for the right ear and an X is used for the left ear to represent the air thresholds. When a bone-conduction vibrator is used to test for thresholds, a < symbol is used for the right ear and a > symbol is used for the left ear. A bone-conduction vibrator is a device that gently rests on the mastoid process of the skull (the bone behind the ear) and is held in place by a small metal band stretching over the top of the head. This device transmits sound via direct vibration of the bone. The vibrations are carried through the bones and tissues and fluids within the skull directly to the cochlea (the hearing organ of the inner ear). This process allows the examiner to bypass the entire outside and middle ear areas and test the sensitivity of the inner ear directly.
By comparing the headphone thresholds with the bone vibrator thresholds at each pitch, we can determine if a hearing loss is conductive, sensorineural or mixed. If the air conduction thresholds show a hearing loss but the bone conduction thresholds are normal, then we call it a conductive hearing loss. If both the air conduction thresholds and the bone conduction thresholds show the same amount of hearing loss, we call it a sensorineural hearing loss. And finally, a mixed hearing loss is when the bone conducted thresholds show a hearing loss and the air conducted thresholds show an even greater hearing loss.
Thus, when the hearing test is completed, the person should be able to tell how well they hear at low, medium and high pitches. If a hearing loss is present, they should also be able to tell which part of the hearing mechanism (the outside, middle or inner ear) is causing the loss.
Ranges have been established to help people identify how much difficulty they should expect from their hearing loss. The typical ranges for an adult are:
-10 dB to 25 dB = Normal range
26 dB to 40 dB = Mild hearing loss
41 dB to 55 dB = Moderate hearing loss
56 dB to 70 dB = Moderately Severe hearing loss
71 dB to 90 dB = Severe hearing loss
over 90 dB = Profound hearing loss.
Audiograms showing the ranges of hearing loss are available.
Because children are not as apt to respond as well as adults, there are different ranges for them. A child may hear the sound, but they may not understand what they are supposed to do. Therefore, they are less likely to give accurate results. Because children's ranges vary according to age and developmental status, they wil not be completely reproduced here.
This article was submitted by:
Glen R. Meier, M.S., CCC-A, FAAA