Downward firing enclosure opinions

Be sure the sub you want to use is capable of down/up firing.  Use the sag calculator.

never gave thought about the "sag" factor of a woofer but i can see the degrading effects that it can have if gravity takes its toll while its playing. guess im building a box to fit there and fire it forward again.

As for the trunk sealing thing, I didnt seal the front of the woofer off completely, just all around it so not much can get out from the trunk into the cabin leaving only the front waves. you can see how i have it setup now on my cardomain page. reason im changing from a fiberglass piece is because ive developed some problems with it warping in one area and it cracked the paint, so i dont feel like going through and making another one.

oooooh, THAT makes more sense now. .

Edit: Ok, to makes sure this is right. The stats of my 12" are as follows:

Fs = 22Hz

Vas = 3.20 cuft OR 90.6L

Xmax = 1.5" OR 38.1mm

Ends up being 1% sag. Im not upset, but that seems kind of low with how beefy the woofer is. I was thinking around 10%.

Your woofer grew a little...it started out as a 8"  ;)

Xmax of 38 mm sounds like it's a full excursion, not a Xmax.  Xmax is one-way, from the resting point to either the neg end or the pos end of the travel length.  This is something that has bothered and confounded me for a long time, because I couldn't find a simple answer to it.  For example, WinISD has a slot in the parameter input to enter the Xmax.  When you look at it, it says "Xmax, peak".  What is peak?  Full excursion both negative and positive, or full excursion from resting point one way?"  (I figured it out that it was the common Xmax:  excursion one way.)

So I looked at different drivers and sort of came to a conclusion over time.  Xmax is the one way excursion distance from the resting point to either + or -.  I looked at the specs of a lot of drivers and noted their Xmax's.  38 is out of the ballpark.  Use half of that  (19mm is still a lot of Xmax)  for the equation.

3% saggy.  Fine for downfiring.  

yeah, they grow up so fast :*) but the 8 was from my last car which i had downfire setup under the dash. going to go with a jl 6 inch nder there this time since thats all i have room for in this car. :(

but i forgot to put one way after the xmax. with given the size of the surround, spider and motor structure, i wouldnt put it past being able to move 1.5" one way with 3"p-p. either way though, youd think itd be fine downfiring it? i just dont want to build the box then have it end up sounding like ass. a second opinion is all i need.

here are the stats from their website, but they havent changed since i got mine. http://www.eclipse-web.com/sw9100/sw9122.html

and since they show the same 12" for almost every sub, these are the correct pictures. the only full ones i have with it out of the box and top view from when I took pictures when my friend was selling his system. well, i snagged the sub. :) and the bottle was for size reference. lol