you could get some form of composite board, similar to what the cabinets are build out of, and go get a cheap comforter from like the Salvation Army or similar (i mean CHEAP, just bulky, who cares if its stained or ripped or whatever) and cut it apart, sew closed the new oopenings, and stable it to one side of these boards
then put those like ears on the speakers, line up one edge with the front edge of the spaeker enclosure
should provide some sound dampening
you could also use a matress (just a matress)
or real speaker insulation
or you could be really really dark, and custom build your own speakers, but don't install woofers, just like 5000W of 20,000hz - ~14,000hz horns/tweeters (yes, it would sound godawful) put it up on a big arm outside your house
then follow this guide:
http://www.rabidhardware.net/index.php?id=42
to save your hearing
then get some music that would sound positively horrible on your new speaker array
some starting ideas:
Brittney Spears
Madonna
anything related to children's music
turn it up as loud as you can go
if your neighbors aren't calling the police inside of 20 minutes i'd be concerned