Air conduction is the normal way you hear. Sound waves travel through the air, enter your ear canal, vibrate the eardrum, pass through three tiny bones in the middle ear, and finally reach the fluid-filled inner ear, where they’re converted into electrical signals your brain interprets as sound. The term comes up most often in hearing tests, where air conduction results reveal how well this entire chain is working.
How Sound Travels Through the Ear
The journey starts at the outer ear, which funnels sound waves into the ear canal. The canal itself acts as a natural amplifier, boosting frequencies between about 2,500 and 4,000 Hz, a range that overlaps with the frequencies most important for understanding speech.
At the end of the canal, sound waves hit the eardrum (tympanic membrane), causing it to vibrate. Those vibrations transfer to three connected bones in the middle ear: the malleus, incus, and stapes, often called the hammer, anvil, and stirrup. These bones do something critical. They amplify the pressure of the incoming sound nearly 200 times before passing it into the inner ear. Two mechanisms make this possible. First, the eardrum is much larger than the oval window (the entry point to the inner ear), so the same force gets concentrated onto a much smaller area. Second, the lever action of the three bones adds further mechanical advantage.
This amplification solves a physics problem. Sound travels easily through air, but the inner ear is filled with fluid. Without the middle ear bridging the gap, roughly 99.9% of sound energy would simply bounce off the fluid barrier. The middle ear’s job is impedance matching: converting low-pressure air vibrations into high-pressure fluid vibrations so the inner ear can detect them.
Once the signal reaches the fluid of the inner ear, specialized hair cells translate vibrations into electrical impulses that travel along the auditory nerve to the brain.
Air Conduction vs. Bone Conduction
Bone conduction is the alternative route. Instead of traveling through the ear canal, eardrum, and middle ear bones, sound vibrations pass directly through the skull bones into the inner ear, bypassing the outer and middle ear entirely. You experience bone conduction whenever you hear your own voice while speaking; part of what you hear reaches your inner ear through your skull, which is why recordings of your voice sound different to you.
Both pathways end at the same place: the inner ear. The difference is where they start and what structures they rely on. Air conduction depends on every part of the ear working correctly. Bone conduction skips the outer and middle ear, so it only tests whether the inner ear and auditory nerve are functional. Research comparing the two has found small loudness differences of about 4 to 10 decibels across various frequencies, with the gap being larger at lower pitches.
How Air Conduction Is Tested
During a standard hearing test (pure tone audiometry), you sit in a soundproof booth wearing earphones. The audiologist plays tones at specific pitches, starting at 250 Hz and going up to 8,000 Hz, and gradually lowers the volume until you can barely hear them. The softest level at which you detect a tone at least half the time is your threshold for that frequency.
Results are plotted on a graph called an audiogram. For the right ear, thresholds are marked with red circles. For the left ear, blue crosses. Thresholds of 25 decibels hearing level (dB HL) or lower are considered normal for adults. If your thresholds fall above 25 dB HL, some degree of hearing loss is present.
The audiologist then repeats a version of the test using a small vibrating device placed on the bone behind your ear. This measures bone conduction thresholds. Comparing the two sets of results is where the real diagnostic value lies.
What the Air-Bone Gap Reveals
When air conduction thresholds are significantly worse than bone conduction thresholds, the difference is called an air-bone gap. A gap of 15 dB or more at a given frequency points to conductive hearing loss, meaning something is physically blocking or disrupting the normal air conduction pathway before sound reaches the inner ear.
If both air and bone conduction thresholds are equally elevated, the inner ear itself (or the auditory nerve) is the problem. This is called sensorineural hearing loss. And if you have a mix of both patterns, it’s classified as mixed hearing loss.
Common Causes of Disrupted Air Conduction
Because air conduction relies on a chain of delicate structures, a problem at any point along the way can reduce hearing. The most common culprits include:
- Earwax buildup, which physically blocks the ear canal
- Ear infections, particularly chronic or repeated middle ear infections that cause fluid to accumulate behind the eardrum
- A ruptured eardrum, which can no longer vibrate efficiently
- Otosclerosis, a condition where abnormal bone growth locks the stapes in place so it can’t transmit vibrations
- Eustachian tube dysfunction, which creates pressure imbalances in the middle ear
- Foreign objects in the ear canal, one of the most common causes of conductive hearing loss in children
Many of these conditions are treatable or reversible. Removing impacted earwax restores hearing immediately. Ear infections often resolve with medication. Even otosclerosis can be addressed surgically. This is one of the key distinctions between conductive and sensorineural hearing loss: conductive problems frequently have a fixable mechanical cause.
Air Conduction and Hearing Aids
Standard hearing aids work on the air conduction principle. They capture sound through a microphone, amplify it digitally, and deliver the louder signal into your ear canal through a small speaker. The amplified sound then follows the same pathway as natural hearing: eardrum, middle ear bones, inner ear. This works well when the issue is sensorineural (the inner ear needs a louder signal to detect sound) or when a mild conductive component is present.
When the outer or middle ear is too damaged or malformed for air conduction hearing aids to help, bone conduction devices offer an alternative. These bypass the blocked pathway entirely, sending vibrations through the skull directly to the inner ear. Some are worn on a headband, while others are surgically anchored to the skull bone behind the ear.