In the audio world, diaphragm refers to the component in a microphone that vibrates sympathetically with air disturbances such as sound waves. It is typically a circular shaped very thin piece of mylar or other delicate low mass material that will range from .2 to 2 inches in diameter. When the diaphragm in a microphone vibrates it generates an electrical signal often by either moving an attached coil of wire in and out of a magnetic gap (in the case of moving coil microphones) or by changing the distance between it and another electrically charged plate (as in condenser microphones). These electrical impulses are then present at the output of the mic and ready for amplification as an audio signal.