Adire Audio, the makers of the Shiva and Tempest, are taking preorders (at a 25% discount) for their newest creation: an 18" sub designed to fit in a sealed box less than 3CF! I hear they are up to 10 orders. Can you imagine popping your trunk and seeing (2) 18"er's staring you in the eyes.
take a look if interested.
http://www.adireaudio.com/cd/maelstrom.htm