Category B - full version without watermark 1024x576 (check terms and conditions at www.teledesign.de) The embed version with watermark is free of charge. The eardrum plays a key role in hearing: sound waves cause the membrane to vibrate. Behind it there is the air filled tympanum with the three ear bones malleus, incus and stapes. They transmit the oscillations to the inner ear to the cochlea. It is filled with fluid; the basilar membrane carries the sensory hair cells. Like sea waves the oscillations make the cells vibrate, the stimuli reach the brain where they are evaluated. However, too much noise damages the ear. The overstressed hair cells degenerate if they don't have enough time to recover. If some hair cells are destroyed sound perception in this area is no longer possible. This leads for instance to a constellation where we can hear somebody talk but cannot understand exactly what he is saying.