I also apologize for the cliche of announcing this is my first Instructable.
While searching on the Youtube, I discovered a video of a man named "Addi" playing an acoustic bass, made entirely out of balloons! In another video, Addi explained how to make one (see below). After watching the video and trying to reconstruct, I determined it was very hard for a boy who could barely blow-up a balloon. So I improvised.
Step 1: Materials
1 - 12 inch circular balloon. This will be the body and resonance.
1 - 12 inch long balloon. This will be the string.
1 small rubber band
Some duct tape
Step 2: Tape the Long Balloon
Step 3: Place Long Balloon in Circle
Step 4: Secure It In
Step 5: Blow, Twist, and Loop!
Step 6: There's a Hole!
Step 7: How to Play
If not, hold the base between your forearm, hold the string in your other hand. Then you basically just pull the string further away to make the pitch slightly higher, and closer for the opposite result. For large changes, pull on the string with your other fingers. As I said, Addi explained it very well near the end of the video.