to pound or not to pound

I currently have a 15" memphis pr dvc in a 2.46 cft sealed box as it is now adjusted within reason i can shake the car and depending on the song rattle the windows in my house alittle, and it still sounds decent aside from my trunk lid rattling like nuts. Now i want more output and some actual air movement from this setup, i'm planning to build a 4.5 cft slot ported box using memphis's white pages  the deminisions are 34x16.5x18.5  with a 14.5x2.5x17 slot port now what i'm wondering is how much louder will this setup be over the current design?  would it be more advisable to just build a bigger sealed box and add a second sub or could i gain some spl by laying some sound dampner in the trunk?

J~

i ve always found that ported boxes are louder if made correctly.  and with a sealed box to get the best proformance you must be specific in the mesure of cubic feet.  Sealed boxes tend to be more proficent at getting the maximum use out of the power.  so there both great choices but if you are looking to get more thump use a ported or a singles reflex bandpass box ( with this last choice you must have your mesurements correct or it wont sound right) You can usually find the alotted cubic feet at the web site of the speakers.