Eardrum vibrations are transmitted to the cochlea by a piston consisting of

ossicles (comprising of hammer, anvil, and stirrup)

Explanation:

The hammer, anvil and stirrup are also known as the malleus, incus, and stapes, respectively which are the part of the middle ear.

They transmit the sound vibrations from eardrum to cochlea by a level mechanism. The generate mechanical advantage by multiplying the force over a shorter distance from the input of a smaller force at a larger distance.