My great 'aha' moment of 'technology is actually sometimes really simple when broken down' was realizing that magnetic sound recording is just running past a sp

My great 'aha' moment of 'technology is actually sometimes really simple when broken down' was realizing that magnetic sound recording is just running past a speaker coil at a constant speed while holding something long and ferrous next to it. To play it back do the same thing but plug the coil into the input.