Question

Once a sound recording is made, how is the sound reproduced?

Answer 1

Depends on the instrument

Explanation:

You could have a digital setup where a microphone (which is a tiny magnet vibrated by a sound wave) stores sound as a group of ones and zeroes which are reproduced through a speaker (which is a magnet that vibrates to create a sound wave).

People have found that moving magnets inside a coil of wire produces current; the pattern of these currents, that correspond to volume, pitch and tempo, can be stored on a digital file. People have also found that passing current through a coil produces a magnetic field which can move a magnet inside it; by passing current through the wire in the pattern dictated by a digital file, you can reproduce a sound recording

On the other hand, you can have a wax-like setup (the thing that Edison stole the patents to).

If you drag a needle on a wax body so that it tries to travel in a straight line but you use sound to disrupt its path, the disrupted path is the same as the sound waves. If you trace the needle over the wax surface, you can (just barely) hear the same sound waves. This is another way to reproduce a sound recording.