I am excited to start building the box for my new 12" BM mkIII but I need a little help.
I took some measurements for the space under the rear seat of my 2008 scab and came up with approx 15.5" wide, 6.5" high (or slightly less because the seat slopes down so the space available under the seat gets less the further back you measure), and 11" front to back (measuring from the edge of the seat to where the floor raises up approx 2inches.

How the heck am I going to get the sub and box under there? I do not want to install a lift on the seat if I can avoid it.
What are the box dimesions that everyone else is using? What thickness MDF do you prefer 3/4 or 1/2"?
Here is a helpful online calculator for determining volume of boxes if you have not found this yet.
http://www.bcae1.com/spboxnew2.htm

 

What I would do is build the box so it extends slightly under the middle portion of the backseat. I don't know how you got 11" of depth because it is much deeper than that. the portion toward the back will obviously be slimmer since the floor raises up a bit towards the back. The box might stick out maybe an inch or so.

Something like this is what I'm talking about. Im sure JJ just slapped this together, but with some more careful design and building I'm sure you can get it to not stick out so much.


I haven't had time to build mine yet but I'll post once I have my dimensions all figures out. I'm going to use all 3/4" MDF but probably 5/8" on the top panel (behind the sub) to help with depth.

 

Im going to try and start mocking this up tomorrow. You are correct that I am going to need to extend it a good bit toward the centerline of the truck under the seat in order to get the necessary size/volume. However there is a hump in the floor under the middle that I will have to contend with. Also another hump in the floor along the back edge way under the seat toward the rear of the cab.
I only saw 1/2" sheets of MDF at Lowes the other day when I was there. I will have to look and see if they also stock 3/4 and 5/8".
I was hoping that you would see this post and respond mSaLL150. I was hoping that you would take some good measurements of your sub box and some photos and I would copy yours however I really want to get this thing running and cant wait much longer!

 

I feel ya man. I'm just as excited to get them in, but taking 20 units and working 2 part time jobs is killing me with time. Not to mention its been raining for the past few weeks nonstop. I'm going to try to whip something up this weekend if the goddamn rain would hold up for just a day or so, although the weather forecast isnt looking good. Its killing me just staring at these beautiful subs sitting in my closet.

What I plan to do is use my current Attrend box as a template since it fits perfectly under the seat. Obviously I will have to build the new box a little wider and about 2" less deep.

Just a FYI Home Depot stocks tons of 3/4" MDF and its pretty cheap.

 

Well that is a quickie box I built. It is 14" deep, 27 wide, 4.5 tall.. I found with the 3/4 mdf, if it is any less than 13.5-14" the basket will hit the walls. Of couse it depends on how you assemble your sides. You would have to shave em. Also due to excursion if it is moved back any farther under the seat the back half of the sub wants to hit on the floor. For that box to fit, the seat pan has to be hammered with a mini sledge, This nets another inch under the seat. The round bar at the back of the seat is not movable and is an issue to get the box farther under. If you can build with angles that would help. I have heard some say an upfire box is easier, I have to disagree because of the floor hump. In order to get the box size you have to do some fancy wood stacking, or angle cuts and glueing in order to get over the hump and keep mount depth. Im no finish carpenter, so for me it is a bit of a challenge. That box I made took 2hrs and is super strong and sealed. It just needs covered for looks. Also the home depot round here doesnt sell 5/8 or I would have used that.

 

What about using 1/2" MDF? It would allow much more volume in the box with a smaller size compared to 3/4 or even 5/8" material.
Is there a problem using the 1/2"? Is it too difficult to screw without splitting the wood or running the screw out the side? Is the box going to come apart years later?

 

The box could flex and or the things you stated with 1/2" mdf..Being it is a small box the internal pressure may not cause an issue. You can try it. Most will advise no. I have an old dual 12" box downstairs that is made of 1/2" particle board. It was always ok. That is from when i was young, so I didnt know the difference.
The box i built fits well, the right height. The sub is as far under as it can go in the pics without exskeetin on the floor. You can angle the front wall a bit to bring it back in.

 

Use 5/8" MDF. Half inch could flex which affects sound and durability, not to mention it'll split easier.

I took some measurements today, both of under the seat and of my existing box.

The BM is only 3.2" deep with the gasket on it, so the box only needs to be ~3.5" deep total. Using 5/8" MDF, this makes the box only 4.2" high total. Also, the BM's cutout is 11.2" so make the internal width 11.5" to keep it safe...with 5/8" MDF this makes the box 12.75" deep total. Then just make it as long under the seat as you need to get .45 or .5 airspace.

Should fit easily as its slightly smaller than JJ's box.

With both subs and taking the center seat bracket notch into account, I calculated my box will be .44 cu ft per sub. With fill, it will be perfectly fine. I've got plenty of EQ on tap anyways.

 

Sall, get er done. One sounded good. Need to know what 2 sounds like.....

 

You must be recessing the top and bottom?Must be, so you need 28 to 29 wide???

 

With internal depth = 11.5", internal height = 2.75" you need internal length = 27.3" to get .5 cu ft internal volume. With two 5/8" MDF sides, the total length is 28.6"

 

Badda bing. I almost went that route. Its a temp box so i just wanted to smack it together. Forgot to mention that the gorrilla wood glue is the shiznit

 

Did you use any screws at all? And did you do that whole box with that Jigsaw? If so then damn you have some steady hands. I'll try the gorrila wood glue, I've used their regular glue and the gorilla tape before and its beast.

I'm going to slap together a box with the dimensions I just posted (well for 2 subs) and test fit it. Then if I feel I can make it fit better I'll build another one. Once I've got it figured out, I'll make a post with the perfect dimensions for under the seat for everyone.

If the weather holds off I'll get it done this weekend and on monday/tuesday.

 

No screws. I stapled the sht out of it with 1 1/2 x 1/4" crown staples with the air compressor. No need for screws. Circular saw for cuts and the jig on the hole..

 

Seal that speaker wire hole! I forgot to do mine on the last box and it made lots of noise.