What is an audiogram?
Hearing tests are usually carried out in an environment which is soundproofed from external noise. The person whose hearing is being tested listens to sounds transmitted by an audiologist and presses a button to signal when they have heard something. The results of the test are plotted on an audiogram.
Audiogram – measuring loudness and pitch
Volume The vertical axis represents volume (loudness) which is measured in decibels (dB). Sounds become louder from the top down – softest near the top of the graph.
Pitch The horizontal axis represents frequency (pitch) which is measured in hertz (Hz). Pitch goes from low (125Hz) on the left to high (8000Hz) on the right – similar to a piano (low notes on the left, higher to the right).
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.
Different severities of hearing loss
Normal hearing is when the softest sounds heard are between -10 and 20 dB. If the sounds are louder than 20 dB and you still can’t hear them, then there is a hearing loss. If the sounds are quieter than 20 dB and you cannot hear them, it may just be that your threshold of hearing is 20 dB. The further down the chart the line of your hearing test comes, the more of a hearing loss you have.
Mild hearing loss is between 21dB and 40dB. You often have difficulty following speech especially in noisy situations. This type of loss is often noticed by family first rather than yourself.
Moderate hearing loss is between 41dB and 70dB. You often have difficulty following speech and other quiet noises. Amplification can be very successful for this loss but you also need to use good hearing tactics (e.g. lipreading, expression, gesture).
Severe hearing loss is between 71dB – 95dB. You are unable to hear speech even in quiet surroundings and do not hear general noises such as traffic unless it’s loud. Amplification can be very successful for this loss but you need to use good hearing tactics (e.g. lipreading, expression, gesture). Lipreading classes will also be very useful if you have this hearing pattern.
Profound hearing loss is greater than 95dB. You are unable to hear most sounds unless really loud. Amplification is often useful but you need to rely on good communication tactics including lip-reading, subtitles on TV and possibly signing.
In the audiology clinic, when testing is done with headphones, we call them ‘air conduction thresholds’ as the sound must travel through the air of the ear canal to be heard.
Alternatively, hearing can be tested using a bone conductor – a device that rests on the bone behind the ear (held in place by a metal band stretching over the top of the head). This bone conductor transmits sound vibrations through the bones of the skull directly to the cochlea. This process allows the audiologist to test the hearing of the inner ear directly.
Right ear Sounds heard in the right ear are marked in red. When headphones are used (air conduction thresholds), they are marked with an O and when a bone conductor is used (bone conduction thresholds), they are marked with a [ or a triangle Δ.
Left ear Sounds heard in the left ear are marked in blue. When headphones are used (air conduction thresholds) they are marked with an X and when a bone conductor is used (bone conduction thresholds), they are marked with a ] or triangle Δ.
Sometimes the graphs of the each ear are plotted on separate audiograms, sometimes they are plotted on the same audiogram.
Audiogram showing right sided age related hearing loss (presbyacusis)
Audiogram showing left sided age related hearing loss (presbyacusis)