I know what I have is nowhere near perfect but up until by amplifier for the sub died, it sounded really good. I had a normal stereo system and added a DIY sub to it. I know you have to build the enclosure to spec, but I was handed the sub speaker for free, had some MDF laying around, and didn't know the specs. So I decided to just wing it just to see how it would sound. To my surprise, it actually sounded great, so I have been using that sub for 5 years now. And btw I do know it's a sub cause it looks like this (not the actual sub):
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