First, make an audio recording of something really loud, and save it to an MP3 file. Since it's so loud, you don't need to turn up the volume on the MP3 player in order to make it play back at the same loudness as the original sound. Like, if the original loudness was 10, you could play it back at volume setting 1 and it'll still sound like 10, in other words, the same as playing back a file with loudness 1 at volume setting 10. But the first case uses only 1/10th the energy (e.g. the MP3 player's battery usage) compared with the second case, see? This implies that the extra energy is somehow STORED IN THE MP3 FILE ITSELF. Like, if instead of hooking the MP3 player to speaker, you hooked it up to a motor, the motor would run just as fast as if the original sound was quiet (then boosted by the MP3 player) as if the original sound was loud (so it didn't have to be boosted by the MP3 player). So all you have to do is post this MP3 file online so lots of copies can be downloaded and played on separate MP3 players across the world. Copying files uses some energy, but not much compared to the original loud sound, surely. So if you play back all of the files at the same time, each using volume setting 1, you'll still get 10 times more energy out than each MP3 player is contributing, just from that one copied file, but now the total quantity of energy is ENORMOUS, enough to run a small submarine or a large hot dog stand.
Think about it.