I plan on 5" of clearance underneath
Downfire ports will be more difficult due to length. So would you recommend rear Fire ports and 3" clearance at bottom? Can always raise it up from theredownfire boxes are slot loading, and add compression to the mix.
this adds group delay, and changes the tune of the porting, especially when using narrowed slot sizing.
5" of clearance brings the amount of compression down and gives a closer tuning to regular boxes, and gives enough space to downfire round ports too, but you may find there isn't enough room in the box to use a straight pipe to port with, to tune as low as you want.
If you drop the clearance to 3" and close off the front opening area, you may find a better response results, as the bass energy is directed towards the rear doors in phase.
Experimenting with clearance heights while leaving the ports the same length, is an easy and fun way to see how the sound changes without making time-consuming adjustments to box volume or port length.
What vehicle are you running the polk in? I'm considering going with just 1-15. It sounded good with one ported. I Have only ran both sealed. The 1 ohm load is killing my electrical. Electrical upgrades are nextOf the choices, I'd say towards the rear doors.
Towards the sides may not allow for enough clearance for the ports and could choke them. Similar may be said of downward as well, though I have no idea what sort of clearance you're shooting for.
I'd vote for NO carpet, you want a solid surface for the subs to load off, not an adsorbent material. Place CLD Tiles in the floor of the truck to reenforce the surface more so, but I'd try without other materials for this location at this time.
I'm running a single Polk MM1540 in a sealed downward firing enclosure and at this point in time, I have 3.5" legs on the enclosure. However I will be testing out 3.75" and finally 4" in the spring.
Still, this is more so my best guess, as I've not dealt with many ported setups.
thats a nice box. mine wont be quite as fancy lol.here is the link to my PB account with pics of building process for 2 x 15" JBL W15 GTI DF box with AEROports facing back
SW BOX Photos by lbaudio_team | Photobucket