Stringed instruments—like Estrella’s viola—need a hollow body, says Chávez. When sound waves bounce around this empty space, they get louder (see Making Waves). The men realized that metal cans or barrels could do the trick.
Chávez and Gómez experimented with different materials to see what worked best. They’ve found they can build wind instruments, like trumpets and saxophones, out of discarded plumbing pipes. They can use bottle caps for keys. To make the skin of a drum, Gómez has used old X-ray film. Hitting the film makes it vibrate, or shake, to produce sound.