Although it does take a fair amount of noise to generate a descent amount of electricity, if you think about it, say you were to harness all the noise from a football game or the hustel and bustel of a large city, by the end of the day you have a lot of power energy. And, while it is of course far from the solution to the plethora of climate problems that faces us--being as impractical and inefficient as it is--the notion of converting sound into electricity is nevertheless in my mind a very neat and fun concept to which very little attention is given.
The things you will need:
1 volt meter
1 speaker (the bigger the better)