box design help

[ducat]

so ive had this audiobahn immortal 10in for a while and im kind of sick of the box and would like to try something new. anyways i want to get the most out of the sub and get as loud as i can. my brother keeps telling me that the sub cant breathe in the box its in now.( dunno what that means) maybe he means because the ports a little small... im just kind of looking for something that will get loud im new to car audio but LOVE it was thinkin of tuning low... my max dimensions are about 28W 28L 20H thanks alot