This homebrew speaker was hacked together from some legos, wire, magnets and a plastic cup — according to the build-log, it "performs very well"!
I didn't expect a high quality of the sound from this made-from-scratch speaker but it performs very well, better than I expected.
A speaker is just a magnet, a coil, frame and a cone or any material that can make the air vibrate. Here is the bill of materials that I used to build this speaker:
# List of materials 1 Magnet (neodymium magnet works great)
# 1 Business card
# Wire 32 or 34 AWG (you may use 30AWG)
# Paper bond
# Ballpoint pen
# Lego bricks or wood.