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Air-bone gap and type of hearing loss calculator

Enter the air conduction and bone conduction thresholds at 500, 1000, 2000 and 4000 hertz to get the air and bone averages, the air-bone gap at each frequency and on average, and the type of hearing loss it suggests.

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Results

Average air-bone gap

33.8 dB

A conductive loss: a gap with normal bone conduction points to the outer or middle ear
Air conduction average
47.5 dB HL
Bone conduction average
13.8 dB HL
Gap at 500 Hz
30 dB
Gap at 1000 Hz
35 dB
Gap at 2000 Hz
35 dB
Gap at 4000 Hz
35 dB

The air-bone gap calculator gives the average air-bone gap, the gap at each frequency and the type of hearing loss (conductive, sensorineural or mixed) from the air conduction and bone conduction thresholds at 500, 1000, 2000 and 4000 hertz.

How the calculation works

  • Enter the air conduction thresholds.
  • Enter the bone conduction thresholds.
  • Read the gaps and the type.

Example

Air conduction thresholds of 40, 45, 50 and 55 dB HL give an average of 47.5 dB HL, and bone conduction thresholds of 10, 10, 15 and 20 dB HL give 13.8 dB HL. The average gap is 47.5 − 13.8 = 33.8 dB, with a gap of 30 dB at 500 Hz. Bone conduction is normal and there is a large gap, which is a conductive pattern.

Why it matters

The calculator helps audiology students, ENT trainees, general practitioners and nurses who read an audiogram and want to understand the type of a hearing loss before the medical assessment.

Good to know

The test is done in one ear at a time, with masking of the other ear when the difference between the two ears is large, since bone conduction is heard by both cochleae and a vibrator on one mastoid can give a response from the better ear if no masking is used. This calculator assumes that the thresholds are correct. A small gap of 5 dB is within the normal variation of the test, and a gap of 10 dB at a single frequency can be a measurement error, while a gap that is large and stable at low frequencies suggests stiffness of the middle ear. The Carhart notch, a dip in bone conduction near 2000 Hz, can produce an apparent sensorineural component in otosclerosis that improves after surgery. The maximum possible gap is around 60 dB, because it is limited by the transmission loss of the middle ear. Treatment depends on the cause and ranges from removal of wax to surgery or a hearing aid, so an ENT doctor should be consulted.

The tympanometry calculator checks the mechanics of the middle ear, the NAL-R calculator treats hearing aid gain, the pure-tone average calculator grades the loss and the ear canal calculator treats canal resonance.

Frequently asked questions

What is the air-bone gap?

It is the difference between the thresholds measured with a headphone (air conduction) and with a vibrator on the bone behind the ear (bone conduction). Bone conduction bypasses the outer and middle ear and tests the cochlea directly.

What does a gap of 10 dB or more mean?

A gap of 10 dB or more, and especially of 15 dB, is significant because test–retest variation is about 5 dB. It points to a problem in the outer or the middle ear, such as wax, fluid, a perforation or otosclerosis.

What is the difference between the types?

In conductive loss, bone conduction is normal and air conduction is reduced. In sensorineural loss, both are reduced by about the same amount. In mixed loss, both are reduced and a gap remains.

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Results are estimates provided for information purposes. They do not replace professional advice.

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