I am running 3 MTX 6124 subs in a sealed enclosure. When they were first hooked up, they weren't very loud inside the car. But if you popped the trunk, it would blow you away. I had my installer cut a hole in the back dash for a port - now it's all good. He said that it's because the trunk is so solid that the bass has nowhere to go - it just cancels itself out. BTW - I've still got my spare, and have the subs facing the opening of the trunk. HTH.