堵耳效应: 特征及成因

Do sounds feel hollow - as if they are produced in a barrel - when wearing earplugs, earphones or hearing aids? Is your own voice loud? Or do you hear boomy sounds when walking or chewing? Perhaps your ears feel clogged or pressured? If you answered yes to at least one of the above, then you are likely experiencing the occlusion effect.

The Occlusion Effect and Its Causes

The occlusion effect occurs when low-frequency sounds are trapped within your ear canals. Tightly-fitting earplugs, earphones or hearing aids can partially or fully block your ear canals. The blockage prevents sounds from escaping the ear and causes them to bounce around in the ear canal, eventually reaching your eardrums and causing you to hear hollow and booming sounds for a while.

But where do the sounds that end up getting trapped originate?

If you are wearing earplugs or earphones, the sounds are caused by vibrations in the skull when chewing, swallowing, walking, or talking. Sometimes, the cause could even be your heartbeats.

If you are wearing hearing aids, they will feed amplified sounds into your ears. Because hearing aids are inserted deeply into the ear and produce loud sounds, it is common to feel occluded when wearing them.

While the occlusion effect is a common culprit causing us to be uncomfortable with the sound of our own voice, it is not the only cause.

Amplusion: Occlusion May Not Be the Whole Story

Occlusion may not be the only cause of your own voice sounding unnatural.

If you are wearing hearing aids with amplification functions, the amplification might interrupt your ability to tune the volume of your own voice.

Because the microphones on hearing aids are close to your mouth, your voice will produce a strong signal. If your hearing aids indiscriminately amplify your voice as if it was someone else's, it will sound overwhelmingly loud and unnatural. At the same time, other people will not hear you clearly if you do not speak loudly enough.

Sometimes, experiencing both amplification and occlusion simultaneously is referred to as amplusion (amplification + occlusion).

If you remain sensitive to low-frequency sounds but suffer from a relatively large hearing loss at high frequencies, then you are at risk of a more severe and annoying feeling of occlusion.

This Factor Is Associated with the Occlusion Effect

Having reviewed research literature on the occlusion effect, we have concluded that the occlusion effect is associated with the frequencies where someone is suffering from a hearing loss.

People with good low-frequency hearing are more likely to suffer from the occlusion effect. The frequency range where the occlusion effect occurs is between 250 and 500 Hz. If you are more sensitive to the lower frequency sounds, then you will perceive that sound more often, causing occlusion.

On the other hand, if you have hearing loss at low frequencies, you are less likely to experience occlusion as the sound may not be loud enough for you to perceive.

Most hearing loss patients would use hearing aids that amplify all sounds, even for low-frequency bone-conducted sounds.

If the wearer is more sensitive to the low-frequency sounds, then he will perceive the amplified sound more strongly, causing the constant loud, hollow noise of the occlusion effect. The more the sound the amplified, the worse the occlusion effect gets, making it unbearable for some hearing aid users.

Improving Music with Occlusion

Occlusion isn’t all bad. For music enjoyers, occlusion may actually improve the sound quality.

Since low-frequency sounds are trapped during occlusion, sounds of instruments with low frequency such as drums or bass will remain longer. This can make music even more enjoyable. Let’s say you want to enjoy the soft bass sound in a song, having occlusion can highlight the bass sound, making it more hearable.