Step 2: Disassemble and Modify Megaphone
After a few minutes of playing with the megaphone, it's time to disassemble. You'll want to pay attention to where the power connections are soldered in the event they break off.
You'll need to desolder the microphone and then solder on a bit of wire - the length of which is based on how far your music player will be from your speaker.
Solder the headphone jack to the opposite end of the speaker.
At this point, you should be able to play music through the megaphone's original speaker.