We live with a dizzying array of electronic devices—cell phones, mp3 players, and DVD players to name a few. Students can operate them with amazing ease, but what do they really know about the basic science concepts used in these technologies? After asking some questions to our fifth-grade classes, we discovered that most students know that electronic devices like cell phones use electrical energy from a battery to produce sound energy through a speaker. However, when we asked them to explain how exactly a speaker makes sound there was a deafening silence! No one had a clue. That was our cue to develop this high-impact activity in which students build, test, and improve their own “coffee can” speakers to observe firsthand how loudspeakers work to convert electrical energy to sound. The activity is appropriate for students in grades three to six and lends itself best to students accustomed to working in groups and who have already done some hands-on investigations with electricity, magnetism, and sound.