OK, I'm removing the factory Bose system from my 1992 infiniti Q45. In each front door, there is currently a 4" speaker in a ported enclosure with a small amplifier board inside. (these enclosures are completely hidden under the door panels). I have removed the enclosures and made plates that cover the hole in the door and have room for the db691 to mount (with plenty of window clearance and no interference with the door panel). I am thinking about enclosing the back of the speaker and an looking for ideas on enclosure volume for the midbass driver in the db691. sealed box? ported box? If I wind up building back-boxes for the front door locations, I will most likely do the same for the pair of db691 speakers that I'm installing in the rear deck. System notes: initially these two pairs of db691 speakers will be running off deck power ("high-power" JVC HD-radio CD player). Eventually I will run an outboard 4 channel amp for these and run an additional amp and sub setup. For now the deck and speakers are all I have the budget for.