Theory behind downfiring box?

[dropkick13 10+ year member]

well no matter what, I'm only going to have about 1.5-2" of space between the sub and floor (downfiring) or sub and seat (upfiring). I realize this is not ideal by any means, but it's a unavoidable sacrifice.

Basically, I'll just go with whichever setup will produce more output. But which will that be? I can see that normally a downfiring setup will have more output but I can't see the sound waves bouncing well off the body of my truck with the 'squishy' carpet in the way muffling the waves. Yes, the seat will be in the way of the sub in an upfiring box but it is basically hollow.

So, with 1.5-2" clearance, which setup will have more output?

 

[nineballsafety8 10+ year member]

it has nothing to do with the distance the enclosure sits from the ground... what you have to think about is the surface area of the opening that the sub it using to transfer the energy into the cabin.

so basically what i am saying is say a box that is 1ft^3 with a ten in it... the box would be 13.5X13.5X13.5, so if you calculate the cone area your looking at roughly 75 sq in. so.... if you take the perimeter of the box (from above) you get 54", therefore your opening needs to be ATLEAST 1.388 in tall. so you would just raise the box up, say an 1.5 inches or so...

so in theory the bigger the box, the less heighth you need to raise the box off the floor...

HOWEVER... in all cases you need to account for the exursion of the driver, so if you do the math and it says your enclosure only needs to be be 3/4" off the floor you are WRONG... your sub needs a MINIMUM of an inch of space to breath when the cone is fully exurted (not sure on spelling)... so if you have a sub with an Xmax of a 1.5 inches you need atleast 1.75 inches of space for you sub to breath (xmax divided by 2= one way excursion plus the inch minimum for your sub to breath)

that is the theory of the how to downfire an sub.