In simple terms there are two forms of deafness; conductive and...

In simple terms there are two forms of deafness; conductive and nerve. A cochlear implant has an external microphone linked to embedded electrodes in the inner ear. In this way it can overcome nerve deafness by directly replacing dead hair cells that would normally respond to sound and send signals to the brain. External hearing aids help best with conductive deafness because they amplify sound. For instance if the connection between the ear drum and the inner ear is bad then boosting the volume helps. They can also to some extent match the frequency pattern of nerve hearing loss but if all the hair cells are dead then a cochlear implant is the way to go.