An audiogram is the graphical representation of the results of pure-tone air conduction tests.
Vertical lines represent the testing frequencies, arranged from low-pitched on the left to high-pitched on the right. Horizontal lines represent the loudness, from very soft at the top to very loud at the bottom.
Audiograms plot the minimum volumes at which a person can detect tones played at each frequency.
“X” is used for the left ear and “O” represents scores for the right ear. The scores are compared to results obtained from persons with normal hearing (i.e. the line at 0dB).
Sometimes the audiogram will also show bracket symbols “[” and “]”. These represent scores based on bone conduction tests. Bone conduction tests bypass the outer ear and middle ear and help identify if there are physical impediments to sound (e.g. structural damage, earwax, blockages due to infection).
Interpreting the Audiogram
An audiologist will use the describe the characteristics of the audiogram in the following ways:
Type of hearing loss
- Conductive – Normal hearing for bone conduction scores ([ & ]), and a hearing loss for Air Conduction scores (X & O). Identifies a blockage, infection, or physical damage within the outer-ear or middle-ear.
- Sensorineural – Hearing loss (equally) for both air and bone conduction (i.e. nerve damage or degradation).
- Mixed – Hearing loss for bone conduction score, and an even greater hearing loss for air conduction scores
Severity of loss
The lower the scores fall on the Audiogram, the more severe the hearing loss.
Slope of loss
- Flat loss – A hearing loss where hearing thresholds (scores) are relatively even across all frequencies. This is commonly indicative of a conductive hearing loss.
- Sloping loss – Increasing degree of hearing loss at higher frequencies. This is the most common hearing loss and is caused by the ageing process and noise damage.
- Other – Less common shapes include reverse slopes, cookie bites, corner audiogram
How the ears compare
- Monaural: Loss is only in one ear
- Binaural: Loss is in both ears
- Symmetrical: Hearing is relatively even in both ears
- Asymmetrical: Hearing loss in one ear is significantly worse than the other ear.
“My hearing is pretty good other than for those high frequencies”
In interpreting an audiogram, it that people misinterpret the results ~ looking at the good news rather than taking in the whole story.
Low frequencies of sounds found in speech (125 Hz – 1000 Hz) are largely responsible for a person’s interpretation of the volume. High frequencies are responsible for clarity. Some of the high-frequency elements of speech include those made by words containing letters such as “f”, “ph”, “th”, “s” and “t”.
Because these sounds are difficult for someone with high-frequency loss to hear, they may often mistake what someone has said. For this reason, many people with greater losses in the higher frequencies commonly feel that: “I can hear ok, it is just that people sound like they’re mumbling”.
Here we can see the audiograms of three people:
- Annie (75 years) – Housewife and grandmother
- Bill (55-years) – Carpenter
- David (12-years) – Passionate cricketer
Presbycusis: Hearing loss caused by ageing process
Annie has a moderate hearing loss that is known as Presbycusis. This results from degradation of the hair receptors (nerve endings) within the cochlear due to the ageing process.
Before she was fitted with hearing aids, Annie always found conversations with her younger grandchildren particularly difficult – especially when in a noisy situation. She also found telephone conversations difficult and noisy restaurants were “simply impossible”.
Noise-induced hearing loss
Bill has been on the tools for 40-years as a carpenter and admits to rarely using ear protection during that time.
His sharply sloping loss in the higher frequencies can be attributed to noise-induced hearing loss caused by electrical saws and other equipment that he has used in his job.
Conductive hearing loss
David is currently suffering from a conductive hearing loss due to a nasty illness that has led to fluid gathering in his middle-ear. He is not hearing very well at the moment and his ears are hurting and “feel tight on the inside”.
This infection is blocking sound through his middle ear. This can be identified by “normal hearing” scores from his bone conduction tests, represented by the “[” and “]”, but a hearing loss in his air conduction results.