First u want to get an old pair of earbuds you don't use.
Next get an old speaker .remember it has to be small enough to fit inside the monster lid.
Now strip the earbud wire with a knife, razor blade or, wire snips. Then sand of a a centimeter off the end of the colored wire and solder it to the speaker. Next u can put electrical tape over the wires or a shrink boot with a lighter.
Find a speaker grill and cut it the size of the speaker and drill out the top of the cap and put in the speaker grill u can hot glue it into the can lid
Hot glue the speaker inside congrats!!!! u now have a monster can lid speaker!!!!