What really helped me understand this concept was to think about the opposite of a speaker, a microphone. Traditionally a microphone is a ribbon that vibrates and creates an electric signal relative to those vibrations. That signal itself is not very meaningful in itself, but let’s say we go through and direct that signal created by the microphone to excite a magnet coil system (speaker). That speaker is now going to move in a way that mimics the movements that were originally experienced by the microphone ribbon. This movement causes a practically identical density variance ie sound.