False Floor/ Spare Tire Well Enclosure

[Chris12]

For years I've been toying with the idea of building a spare tire well enclosure. My current setup is awesome, but I'd like more output and I'd like to regain the ability to pass luggage from the trunk into the rear seat.

I currently have an IB setup with an AE SBP15 residing in a wall between my trunk and rear seat. And, on the rear wall of my parcel shelf, I have an amp rack. These are the two equipment groups which I'll be upgrading and detailing in this build:




First, my current setup:

Amps
2@ JL XD400/4 (one for tweeters and mids, the other for MB's)
1@ JL XD300/1 (Sub)

DSP
Minidsp c-dsp 6x8

HU
Kenwood DDX-9905s

Front Stage
Tweeters - ScanSpeak D3004/604010 Large Chamber Be (I was able to fit these so I went with them over the small chambers).
Mids - Dyn Audio Esotar²..430
MidBass - JL ZR800

Sub Stage
1@ AE SBP15



Heres what I'll be upgrading to in this build:

New Amp Setup
2@ JL HD900/5 (one for Left Front Stage and one for Right Front Stage)
2@ JL HD1200/1 (one for each Sub)

New Sub Setup
2@ Illusion Audio Carbon C12 XL

[Chris12]

First step was to cover the area with CLD. (I’ve also covered the bare sheet metal spots in since I took this photo). Then I added M8 rivnuts to hold everything down.




Then I decided to get an approximate volume of the spare tire well. First I calculated a theoretical volume by using the size of the spare tire as reference which had a 28" (2.33') overall diameter, and an 8" (0.667') width. So, using the formula 0.785 x Diameter squared x height/width (0.785 x 2.33' x 2.33' x 0.667') I got a theoretical 2.84 Cubic Foot total.

Not comfortable with just the theoretical calculation, I found my daughters old "bean bag" chair in the garage and cut that sucker open


I used a one quart measuring cup and scooped the beads in until the spare tire well was full and flush with the rest of the trunk floor (so a bit higher than you see in this photo). I ended up with 85 quarts which amazingly is 2.84 cubic feet, the same exact number I calculated theoretically. I had no idea what the conversion of quarts to cubic feet was until after I had already scooped all the beads into the spare tire well and got my total in quarts, so there was no confirmation bias at play here.

Then I made a foundation board to hold the enclosure and amp rack to the vehicle. Its held down with six black oxide M8 bolts. (sorry for the blurry image):


Next I added two 1/2 pieces of MDF (which I later glued together) for the fiberglass to adhere to:
First


And Second:


Then a 3/4" piece of MDF with a 1/2" inlay for the top layer of the baffle:

[Chris12]

Then I taped off the area to be fiberglassed with aluminum tape:







I've never fiberglassed anything this big or anything where the strength mattered much, so I gave a fair amount of thought as to what materials to buy. I contacted US Composites and they gave me recommendations based on my project.

Heres what I bought:
- 2 Gallons of 404 Tooling Polyester Resin. (They recommended this over the 435 Standard Layup resin which I'd used in the past)
- 4 Yards of 1708 Biaxial Mat Knytex. (I'm very glad I went with this over anything lighter weight. This stuff is STRONG and very workable)
- Partall #2 Paste Wax. (I'd skip this if I were buying today and just use carnauba wax on the mold)
- 1oz. Carbon Black Pigment (Many of the pro guys use this to color the resin. I really helps to see air pockets when wetting out plus it looks great)
- 2 yards of 1.5 oz. Chopped Strand Mat (I should've bought more of this..)

For my initial layup I used 2 yards of 1.5oz CSM and one layer of biaxial mat. Then I placed it back in the car and added an additional two layers of biaxial mat.



Next I milk-shaked all the seams and the entire inside and outside of the enclosure. This made everything air-tight, added mass and greatly strengthened the fiberglass to MDF bond.

[nadams5755]

sounded quite good before, i'm excited to see how this turns out.

[Chris12]

I’ve made a bit of progress on this project.

I sprayed the entire underside with a rubberized coating. I wanted to ensure that everything was sealed and it’ll help with resonances a bit:


Also added some top to bottom bracing. I had planned on building a wall down the center to separate the two subs air space, but I had some complications. The primary issue was that I wanted to use the center oem tie down for the enclosure as its much stronger than the rivnuts I put into the sheet metal.
Anyhow, here's the bracing. the scraps at the very top are just for alignment:


Next I re-measured the internal volume to see where I was at. I ended up right in the area where I wanted to be for the two c12xl's - right around 80 quarts or 2.67 cubic feet.


With the internal volume confirmed, I pulled the bracing and added CLD to the entire inside surface. Fiberglass is known to resonate so this was another step to deaden the enclosure:

[Turb0Yoda]

god damnit I've been missing the same ability - to the point of wanting to glass a box for the brahma and move all my gear somewhere else.. this just makes that temptation stronger - sad to see the IB go.

[LBaudio]

Al this fabricating turned out great! I like how clean your process and product is!

[Chris12]

Its been hard for me to get work done on this project. My kids have gone back to school (physically) and their schedule has me driving back-and-forth to their respective school about every two hours throughout the day (four round trips).

Anyhow, I figured I'd post an update.



Over the past two weeks I've bought a few more items for the project:

O) - JL HD1200/1 used. The Used (and new) inventory on JL Amps has been drastically reduced since the last big stimulus.
O) - 100' 14 AWG OFC Speaker Wire (Sky High Car Audio/ SHCA)
O) - 25' 4 AWG OFC Power/ Ground Wire (SHCA)
O) - 1/0 AWG Wire Splitter. 1@ 1/0 or 4 AWG in, 2@ 1/0 or 4 AWG out. This will go on my power wire just ahead of my Audison SFD41C dist. block.



On to the physical progress..

I got all the bracing glued in. I used Gorilla Glue Epoxy, Titebond III, and stranded filler milkshake to adhere everything.





Next, I got the top glued on. I started with Titebond III wood glue, then filled the gaps with 1/4" fiberglass strands (where they would fit) and resin. Finally, I leveled it off with bondo.



Next, I fabbed the baffle. Its made from two @ 1/2" MDF and two @ 3/4" MDF. The the 1/2" at the bottom is really a spacer and the 1/2 at the top insets the sub. The baffle itself which the subs bolt to is two at 3/4" MDF:





And with the C12XL's in:

[Chris12]

It’s going slow, but I did make a bit of progress:

Amp rack cut from 1/2” mdf:



Rough amp layout. (Used different orientation of the amps in final version):


Amp rack wired up:

[DavidRam]

That stuff's gonna be like cocaine in Cali...