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Air-Bone Gap - What’s That?

by Neil Bauman, Ph.D.

A man wrote:

After three years of badgering, (and constant reminders that I was getting tired of repeating myself) my 84 year old aunt finally went to an audiologist for a hearing evaluation.

Upon finishing the audiogram, she was told to go see an ENT, in order to have her “Air-Bone Gap” evaluated. I’ve never heard of an air-bone gap before. What the Sam Hill is it anyway?

Good question. The reason for this strange and oxymoronic-sounding term, and the cause of your confusion, is that this term is really just a contraction audiologists use instead of saying, “The results of your air-conduction hearing tests and the results of your bone-conduction hearing tests don’t match each other because your air-conduction tests gave much poorer results than your bone-conduction tests.”

The difference (or gap) between these two lines plotted on your audiogram is the air [conduction] – bone [conduction] gap or air- bone gap for short. For example, if your audiogram showed an air- conduction hearing loss of 70 dB while your bone-conduction test results only showed a 40 dB hearing loss for a given test frequency, then the difference between them in this case would be an air-bone gap of 30 dB (70 – 40 = 30).

In case you are interested, air-conduction tests evaluate your ability to hear sounds traveling through the air in your ear canals, then vibrating your ear drums, which in turn vibrate the three tiny bones in your middle ears and then transmit these vibrations via the oval window to your cochlea.

In contrast, bone-conduction tests evaluate your hearing by placing a bone oscillator (vibrator) on the mastoid bone behind your ear. This directly vibrates your skull and thus your cochlea, which is embedded in your skull - thus effectively bypassing your ear canal, ear drum and middle ear bones.

If there is a difference between the air-conduction and bone- conduction test results, this indicates problems somewhere in your outer or middle ears. This could be something such as wax (or “junk”) in your ear canal blocking incoming sounds, a hole or other problem in your eardrum, fluid in your middle ear, damage to your middle ear bones (for example—otosclerosis), etc.

That is why if there is an air-bone gap you typically want to see an ear specialist to find out why. The good news is that often these kinds of problems can be fixed by an ear specialist...

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