.

Hearing tests & audiograms

Webpage published: 2011/Last reviewed: 2012

 

Hearing tests and audiograms explainedWe explain what happens when you have a hearing test and how to interpret different audiograms: 

Different types of hearing loss

 

There are two main types of hearing loss:

  • A conductive hearing loss is where the problem lies in the middle ear - ear drum or ossicles. A conductive hearing loss makes everything sound the same, just much quieter. More about conductive hearing loss.
  • A sensorineural hearing loss is defined as damage to the hair cells in the cochlea (this is the sensory hearing organ) or damage to the neural pathways of hearing (nerves). It is not always possible to tell which part is damaged, so these are therefore often listed together as sensorineural hearing loss. Sensorineural hearing loss causes speech to sound quieter and distorted. More about sensorineural hearing loss.

Hearing loss in one ear is called a unilateral hearing loss, in both ears it is called a bilateral hearing loss.

The structure of the ear

What people hear with different types of hearing loss

Very few people who have a hearing loss hear nothing at all. Many people who are hard of hearing or deaf hear some sounds, but what varies from person to person, is how much they hear and the clarity of what they do hear.

People who have conductive loss hear sounds, but they are softer (volume is reduced) and want people to 'speak up'. People who have sensorineural hearing loss on the other hand, lose both some volume and also a degree of clarity; typically they 'can tell that someone is talking, but can't understand what they say'.

Understanding the 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.

The audiogram gives information used to determine the most suitable help for an individual - which could be a hearing aid, cochlear implant, or other supportive device or equipment.

Audiogram - measuring loudness and pitchAudiogram

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 lossDifferent severities of hearing loss plotted on an audiogram  

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 lipreading, subtitles on TV and possibly signing.  

The speech banana

 

A useful way to look at the audiogram is to superimpose a ‘speech banana’ on it. The speech banana is so called because of its shape. It represents the intensity and frequency of sounds of speech or ‘phonemes’ in language, which when placed on the audiogram, form a banana like shape.

In adults hearing loss within the speech banana can have serious implications on the person's ability to follow what is being said to them (speech discrimination).

Speech banana

Speech banana

Image source: Phonak

The hearing test and audiogram

 

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 age related hearing loss

Image source: Bay Area Audiophile Society web site

Looking at the audiogram above, we can see that sound at 2000 Hz would have to be 40 dB loud before it could be heard in the right ear (O), and about 37 dB for the left ear (X).

Different audiograms

 

Different kinds of hearing loss have differently shaped audiograms. By comparing the air conduction thresholds (O or X) with the bone conduction thresholds ([, Δ, ] or Δ) at each pitch, we can determine if a hearing loss is conductive or sensorineural.

Some examples are given below:

Conductive deafness

If the bone conduction levels differ from the air conduction levels, sound waves are probably being obstructed on their passage through the eardrum and middle ear. This audiogram shows a right sided conductive hearing loss, possibly caused by perforation of the eardrum or 'glue ear' (congestion behind the eardrum which is common in children).

Audiogram showking conductive hearing loss

Sensorineural hearing loss

If air and bone conduction are the same, it indicates that the problem is likely to be located in the inner ear. We call this a sensorineural hearing loss. The audiograms below show (a) bilateral mild sensorineural hearing loss and (b) bilateral moderate sensorineural hearing loss.

(a) Bilateral mild sensorineural hearing loss  

Audiogram showing bilateral mild sensorineural hearing loss

(b) Bilateral moderate sensorineural hearing loss

Audiogram showing bilateral moderate sensorineural hearing loss

Age related hearing loss (presbyacusis)

The audiograms below show bilateral (both ears) age related hearing loss. With age related hearing loss a person can usually hear low-pitched sounds better than high-pitched sounds. Clarity of sound is affected - 'I can tell that someone is talking but cannot understand what they have said'.

(a) Right sided age related hearing loss (presbyacusis)

Audiogram showing right sided age related hearing loss       

(b) Left sided age related hearing loss (presbyacusis)

Audiogram showing left sided age related hearing loss

Hearing loss caused by Menieres Disease      

Typically, the audiogram of someone with Menieres Disease slopes from right to left. Thus, the person with this audiogram will be able to hear high-pitched sounds better than low-pitched sounds in the left ear. The right ear hears perfectly.

Audiogram showing Menieres Disease

So, if you have a moderate sensorineural unilateral hearing loss caused by infectious parotitis don’t panic. It is just the medical way of saying you have nerve deafness in one ear caused by mumps and have problems hearing sounds which are quieter than 41dB. 

Please do not be afraid to ask the ENT doctor or audiologist to explain your hearing chart to you.

Hearing Link Registered Charity Number 264809 Registered Charity Number in Scotland SC037688