My local newspaper (Charleston's Post and Courier) had a blurb in the comics section this week that mentioned a good resource for kids (at heart) to learn about audio. It is the Listen Project and can be found on the Exploratorium's website. It seems to live up to its tag line of "Explore the art and science of listening". I highly recommend it.
To give credit where credit is due - the project is funded by the National Science Foundation, the Gordon and Betty Moore Foundation, The Bernard Osher Foundation, and the National Endowment for the Arts.