1 Answers
The occlusion effect occurs when an object fills the outer portion of a person's ear canal, causing that person to perceive echo-like "hollow" or "booming" sounds generated from their own voice.
The bone-conducted sound travels to the cochlea through different pathways. The outer ear pathway corresponds to the sound pressure generated in the ear canal cavity due to the vibration of the ear canal wall, which constitutes the source of the occlusion effect. At low frequencies, the outer ear pathway is negligible when the ear canal is open but dominates when it is occluded. The occlusion effect is thus objectively characterized by an acoustic pressure increase in the occluded ear canal at low frequencies and which can be measured with a probe-tube microphone.
Considering that the vibrating ear canal wall acts as an ideal source of volume velocity , the occlusion device increases the “opposition” of the ear canal cavity to the volume velocity imposed by its wall and thus increases the amplitude of the acoustic pressure that is generated in reaction, leading to the occlusion effect.
The acoustic impedance of the ear canal cavity represents its “opposition” to the volume velocity transfer and governs its reaction in terms of acoustic pressure. In other words, the occlusion effect is mainly due to the increase of the acoustic impedance of the ear canal cavity when it is occluded.