Which part of the ear increases the size of the vibrations of sound waves entering the ear?

The part of the ear that increases the size of the vibrations of sound waves is the inner ear.

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Middle ear

The eardrum is very thin, measures approximately 8-10 mm in diameter and is stretched by means of small muscles. The pressure from sound waves makes the eardrum vibrate.  

The vibrations are transmitted further into the ear via three bones in the middle ear: the hammer (malleus), the anvil (incus) and the stirrup (stapes). These three bones form a kind of bridge, and the stirrup, which is the last bone that sounds reach, is connected to the oval window.

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