Originally Posted by tntahoe
I assume the middle graph is what you want
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Personally... I'd want the leftmost one. That's the box 50% larger than "recommended".
The middle one is optimum, the shallow response one is the 50% smaller than optimum. You can see the slight peak in the middle of its response. The smaller you go with that box, the more pronounced that peak will get.
At some point, you'll get too big and you'll lose control of the sub though. Basic models can only tell you so much. Some software can predict how much power a sub will take to reach xmax. That's useful to know depending on your setup and when you can get it to max output.