The drum you always hear
Your eardrum vibrates in response to the pressure fluctuations associated with a sound wave. The amplitude of the oscillations associated with audible sounds is surprisingly small. The figure above is an animation of the eardrum. The schematic below illustrates how the oscillations follow the pressure in a sound wave.
Reference:http://www.glenbrook.k12.il.us/gbssci/phys/mmedia/waves/edl.html
Reference:http://funsan.biomed.mcgill.ca/ funnell/OpenHouse96/midear_anim.gif