I purchased an underdash sub box and a JL 8w3 to go in it. The 8W3 says it requires .3cuft of airspace. I drew up the sub box in autocad and calculated the internal volume and found it to be shy of the required .3cuft requirement. The internal volume was just over .2cuft but once you calculate in the displacement of the woofer it makes it almost exactly .2cuft. I proceeded to then build my own .3cuft box, just your typical cube box just to see how it sounded compaired to the purchased underdash sub box. What I found was the .3cuft box was much better sounding, both cleaner and louder. I'm not posting this to encourage people to stop buying the underdash sub boxes, but for someone to come up with a way to make an underdash sub box that has an internal volume of .3cuft for an 8" sub. If someone were to do this I would definitly purchase one from them. Don't get me wrong the underdash sub box I purchased sounds good but there is still more potential there.