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How we measure hearing loss

Hearing can be measured in different ways.

It can be done by testing how well someone understands speech either at normal voice levels or whispered. However, there are two key problems with this type of testing.

First, it is difficult to maintain constant intensities of speech and second, because speech is made up of many sounds that differ widely in frequency or pitch, a hearing loss that is mainly confined to a particular frequency region may be missed. So most audiologists measure hearing by using test techniques that provide sounds of known intensity and specific frequencies.

Test - headphonesTo ascertain the type of hearing loss, hearing is measured using earphones (which measure air conduction) and by placing a small vibrator on your head (which largely bypasses the eardrum and middle ear and measures the sound waves that pass directly to the cochlea in the inner ear) and this measures the overall efficiency of your hearing.

With the earphones, the listener is provided with tones of different frequencies, testing one ear at a time. The intensity of each tone is varied to find the lowest level that the listener can hear, which is then described as the threshold for that tone.

It is unusual for someone's hearing threshold to be the same or similar for different frequencies - usually there is a greater hearing loss for high frequency tones. Equally, hearing loss can be different in each ear. We measure hearing loss in units called decibels hearing level (dB HL for short).

Also see:   What happens during the hearing test?

After your hearing test, your hearing aid audiologist will plot the results on a graph and use the measurements to tell you the extent - if any - of your hearing loss.

Mild hearing loss

20-40 dB HL    You cannot hear soft sounds and you struggle to understand speech in noisy places. 

Moderate hearing loss

41-70 db HL    You cannot hear moderate sounds and have difficulty understanding speech when there is background noise. 

Severe hearing loss

71-95 db HL    You have to ask people to raise their voices and group conversations are extremely difficult. 

Profound hearing loss

More than 95db HL    You can only hear some very loud sounds and communication is impossible without hearing aids.