Here is a link to a video about using sheet lead as a speaker enclosure.
This fellow has some more examples of different speakers if you know how to search the You Tube videos. He is a contributor to the Yahoo SoundTraxx group.
Yes, I know all about the potential health issues about handling lead and having it around the house where there are young children.
I use sheet styrene for enclosures.
http://www.youtube.com/watch?v=6zfuBNJyvlM
Rich