The sound is SO much better with the cover off. I agree with cutting the stock cover so the sub can breath. It also sounds much better after playing for a few hours to break in.

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2003 4.6is, Saphire Black on Black with Aluminum trim, Comfot Seats, Loading floor, Nav, TVonNav, Focal Utopia's in front, with Rainbow's in back, Helix 5 channel amp. ACS pedals, Aluminum steering wheel trim, X-pipe