Meet the HUMBIRD: a bone conduction speaker that turns any hollow surface into a speaker. It delivers sound up to 115db and can be used as a pair to deliver a surround sound experience. You can test the speaker on various surfaces to find the tone that you like.
This speaker only weighs 35 grams and is small enough to fit in your pocket. Expected to ship in August. You can find out more about it on Indiegogo.