Air Conduction and Bone Conduction: The Two Routes Sound Takes to the Inner Ear

Put your fingers in your ears and hum. The hum gets louder, not quieter. Crunch a piece of toast and the noise inside your head can seem enormous, even though the person next to you barely notices. These everyday oddities point to something easy to overlook: sound has more than one way into the inner ear.

What is air conduction?

Air conduction is the route most people picture when they think about hearing. Sound travels through the air into the ear canal, sets the eardrum vibrating, and is passed along the chain of tiny bones in the middle ear to the cochlea. Each stage adds something. The outer ear shapes the sound, the canal boosts some pitches, and the middle ear helps vibration cross from air into the fluid of the inner ear, a process explained in the middle ear.

Nearly everything you hear from the world around you, from conversation to birdsong, arrives mainly this way.

What is bone conduction?

The cochlea is embedded in bone, deep inside the skull. When the skull itself vibrates, those vibrations reach the cochlea directly, without needing the ear canal, eardrum or middle-ear bones. This second route is bone conduction.

For sounds coming from the air, bone conduction plays only a small part, because it takes a lot of energy to make the skull vibrate noticeably. But for sounds that start inside or against your head, it becomes very important. When you speak, your vocal cords and the air in your throat and mouth set the bones of your head vibrating. When you chew, your jaw does the same. That is why your own voice and your own chewing seem so much louder to you than to anyone else.

The two routes also interact. Normally, part of the low-pitched energy from your own voice escapes out through the open ear canal. When you block the canal with a finger, or when it is filled by something like an earplug, that energy is trapped. It bounces around the closed space and adds to what reaches the eardrum. The result is a boomy, hollow version of your own voice.

Specialists call this the occlusion effect. It is a neat demonstration that air and bone routes interact rather than working in isolation. It also explains why people often notice their own voice first when something changes in the ear canal.

How do hearing tests use the two paths?

Because the two routes share the same destination but take different paths to get there, comparing them is very informative.

In a standard assessment, tones are first played through earphones, testing the full air-conduction route. Then a small vibrating device is placed on the bone behind the ear or on the forehead, sending tones straight to the cochlea by bone conduction. The tester records how soft each tone can be on each route. You can read about this and the other parts of an assessment in hearing tests explained.

The comparison works roughly like this:

• If bone-conduction hearing is good but air-conduction hearing is reduced, sound is being held up somewhere in the outer or middle ear, while the inner ear is responding well.
• If both routes are reduced to a similar extent, the issue is more likely in the cochlea or hearing nerve.
• A mixture of both patterns suggests both parts may be involved.

These patterns correspond to the categories in types of hearing loss. Doctors sometimes make a quick, simple comparison of the two routes with a tuning fork during an examination, before any formal test.

Is bone conduction used outside the clinic?

Yes, in a general way. Some headphones rest on the cheekbones instead of covering the ears, sending sound through the bone while leaving the ear canal open to the surroundings. People use them so that they can still hear traffic or conversation around them. There are also medical devices that use bone conduction, which a professional would discuss in the context of a person's own hearing. The principle is the same: vibration delivered to the skull, heard in the cochlea.

Key takeaways

• Air conduction is the usual route: ear canal, eardrum, middle-ear bones, cochlea.
• Bone conduction carries vibration through the skull straight to the cochlea.
• Your own voice and chewing reach you largely through bone conduction, which is why they sound louder to you.
• Comparing air and bone results helps show whether a problem is before or within the inner ear.