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If you have shallow mount subs, then most likely they are meant for a sealed enclosure. I am also guessing you got shallow mount subs for space conservation reasons. A ported enclosure is normally larger than the sealed enclosure for any given subwoofer. The sub requires more airspace, as well as port space in this application. Rockford Fosgate has good literature included with their speakers as to how to make them perform best. Read it, and do what they say.

Sealed will give crisper sound than ported, but in my opinun a sub is for bigger sounding bass that you can also feel from a ported enclosure.

Sealed gives them a more cleaner sound but ported makes them sound way louder and moves more air. I like ported better than sealed.

sealed gives a crisper slap..ported moves more air making them sound louder