A Conductive Hearing Loss can occur if the External Auditory Meatus is obstructed.
The External Auditory Meatus functions clearly as a passageway to conduct air (sound) waves into the middle ear. Anything that interferes with this canal will hamper the hearing process.
I see students in class putting their fingers in both ears quite frequently during parts of the lecture. The result for them is a reduction of the loudness of sound. This is referred to as a Conductive Hearing Loss. There are three interesting facts about a conductive hearing loss.
(1) It is impossible to be deaf with a conductive hearing loss. The most you could hope for under any circumstance is a 60 dB loss.
Hence, if I put my mouth right next to a person with their fingers in their ears and talk reasonably loud (over 60 dB), they will still hear every word of the lecture.
Not only will they hear it all but the (2) fidelity will be normal. That is, there will be no distortion of my somewhat high shrill nasal voice.