Certain crystals change their electrical properties as they change shape (see How Quartz Watches Work for one example of this phenomenon). By attaching a diaphragm to a crystal, the crystal will create a signal when sound waves hit the diaphragm.
As you can see, just about every technology imaginable has been harnessed to convert sound waves into electrical signals. The one thing most have in common is the diaphragm, which gathers the sound waves and creates movement in whatever technology is being used to create the signal.
For more information of music technology and other cool gadgets, see the next page.