Why do some people feel echo after wearing hearing aid?

After wearing a hearing aid, some people may feel their words echo and hum like they are speaking in a barrel, even before the switch is turned on.This is because the ear mold (including the customized hearing aid shell) will be closed external auditory canal, their voice through the middle ear and skull conduction caused by the vibration of the cartilage of the external auditory canal.Normally without a hearing aid the external auditory canal is open and this vibrational energy is released undetected.When the external auditory canal is closed by the ear mold, this energy is retained in the external auditory canal to produce this phenomenon.Another way to explain it is that the sound of our own voice on a tape recorder is “strange” to us but not to others.Why is that?Because normally we hear ourselves speak, both through the mouth and through the outer ear to the inner ear “air” component, and directly through the skull vibration to the inner ear “bone” component.When we listen to a tape recorder, we can only hear the air conduction component, not the bone conduction component.Under normal circumstances, the “air conduction” and “bone conduction” components are in balance.We take it for granted.If you put on a hearing aid and you have a sudden increase in the bone conductance, you will hear an echo.

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