Cymatics: Demonstration using salt

Cymatics is the study of the effects of sound waves on physical items. Such as water or in the case of the video above, salt. The amazing thing is the patterns formed in the loose salt by nothing but the sound waves. The sounds in the video are actually pretty jarring. So you may want to keep the volume on your speakers on low.

Via Neatorama: The Effect of Sounds Waves on Salt

Cardboard Sound Room

I have no idea who made this, as the article doesn't say. But I guess you could make it yourself if you had a large quantity of cardboard sheets. Basically it's a stack of cardboard sheets that has had a room hollowed out of it. Then a stereo system and speakers installed in it. It seems that the acoustic properties of corrugated cardboard make for a good listening experience.
But I think it is just cool to have a adult sized cardboard room to play in. Remember when you were little and you used to take the cardboard boxes from large appliances to build rooms and houses? Well, if you didn't you really missed out. My siblings and I once built an entire maze out of discarded boxes left over after moving into a new house. We had tons of fun with it until Mom made us throw them out to make room for our furniture.

Via The Cool Hunter: Cardboard Sound Box (A place for listening)