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...

 

[Chris12]

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

Seriously

Anyone needs their fix, let me know. I may be able to let a can or two slide.. just $100 a pop

 

[nadams5755]

Heres the 1/0 power wire which will run from the battery fuse to the positive battery terminal. I used black adhesive lined heat shrink for everything under the hood as I wanted it to look factory. For anyone reading (Nick ) Would this be frowned upon if I ever entered a competition?

appropriately sized wire, fused within 18" of the battery, and grommets where wires pass through metal are the usual requirements

many people elect to cover the wires for additional protection and aesthetics. if you want to compete install, people go nuts to maximize points.

 

[Chris12]

There will come a day (very soon) when I'll need to swap all my in-car speaker wiring over to my new amps (lengthen/re-route). So basically, I'm reaching a point to where I need to commit to getting some things done or I'll receive the punishment of silent car rides

I loosely scheduled a tuning session for the end of the month with Nick A. Another motivation to, at the very least, get this new system online, and possibly even the motivation to actually get this project done (probably not ).





Some updates:



I covered the underside of the fiberglass enclosure with 1/8" CCF to decouple:

Also covered both sides of foundation board w/ CCF:

Added CCF and a spacer (for the area that extends past the foundation board) to the amp rack:

Ran speaker wiring for the subs. I sealed the underside with "duct seal" and used clear silicone for the rest. Inside the enclosure I wrapped the speaker wire with CCF tape and then wrapped the that with Tesa 51036 (excellent stuff):

Up to this point, the sub enclosure was only held down with one M8 bolt at the very center, which formerly was used to hold the OEM spare tire in place. I added three more 1/4-20 screws which go through the amp rack and enclosure and thread into inserts I epoxied into the underside of the foundation board. With these four screws (in total) the enclosure/amp rack is mounted very securely to the car.

And lastly, I've got the subs ready to play at 4 ohms

 

[Chris12]

A few more updates.

After using a MiniDSP C-DSP 6x8 for around three years, I decided to upgrade to a Helix DSP.3. With the DSP.3 I'll gain higher voltage output and more tuning channels. The Helix is currently being shipped and is scheduled to arrive late next week.


I currently have the MiniDSP mounted to a piece of ABS, tucked up beneath my trunk lining. (The messy wiring shown here is just temporary as I transition my old setup to the new ).
With the new DSP.3 I'll need to decide if I'm going to mount it in the same spot as the miniDSP, or mount it to the amp rack for a more centralized equipment location and easier serviceability. I currently have six foot stinger 6000 interconnects running from the DSP output to the amps. I'd likely need to get shorter RCA's, or even make my own custom lengths if I moved the DSP. We shall see..

I set the gains on the new amps (which I'll need to re-do once the DSP.3 arrives ) and got the subs up and running.
Everything isn't tuned properly yet, but I've heard enough to say that the C12XL's are output monsters .
I'm definitely happy I went with them over the other options I considered (brahma, w7, etc.)

I sprung for some pretty nice Blue Sea Systems 30a barrier strips. Total overkill, I know, but they came in handy when setting my gains (vs the cramped speaker terminals on the side of the amps ). I know setting the gains through additional points of failure wouldn't stand up to the Occam's razor school of thought, but everything seemed to work out just fine. Especially considering that this gain setting session was nothing more than a practice run with the new DSP on the way

After deciding to go fishing with my kids yesterday, and sweating over the fishing pole being in close proximity to my unprotected $1K+ subwoofers- I decided to put these grills on that I had sitting around. They aren't a permanent fixture, but they'll work fine as protection until I complete the false floor setup. As you can see, the grills have a bulge to them, and they're mounted on MDF which is 1/2" higher than the sub flange, so hopefully they won't limit excursion on these monsters.

 

[Chris12]

I bought a couple things.

Blue Sea Systems 6 circuit fuse block with ground. At the absolute most, I’ll only use four of these circuits. (DSP, 2@ LED circuits, and MAYBE HU). But, I found this on Amazon as a return for $18. It was worth it to me to have the fuse distribution and grounds all in one nice neat package (3.5” x 5” )

And the Helix DSP.3:

View attachment 16030

 

[nadams5755]

we put some ears on it today, it sounds fantastic.

 

[Chris12]

Nick got my system all dialed in yesterday, and it sounds AMAZING! It is, without a doubt, a night-and-day difference from what it was before. The upgrades/ tune certainly corrected everything I felt was lacking.

As a quick summary: I changed my amps, DSP and subs. My entire front stage/ front stage install remained exactly the same as before. Nick also tweaked the way he tunes - we set the crossovers, levels, and most of the EQ from outside the car (with the mic stuck in the head rest). It now has that powerful sound and output that I was looking for, and has a really good sense of space and room. I still have some resonances in my driver door, but I'm hoping to work it out with some install modifications in the near future.




Before/ After available power:

ScanSpeak D3004/604010: 75w rms before/ 200w rms after
Dyn Esotar 430: 75w rms before/ 250w rms after
JL zr800: 175w rms before/ 539w rms after

Sub: 1@ AE SBP15 x 250w rms before/ 2 @Illusion Audio c12xl x 1288w rms after

Heres what we started with yesterday:

And here's our midway point. After this we didn't take any more measurements, Nick did everything by ear:

Thanks again for everything Nick! You're making the world a better place - one stereo at a time

 

[Chris12]

I modified the shape of the amp rack a bit to allow a slightly different configuration of the components and make installation/removal of the rack itself easier (decreased width). While it was out, I also painted it black.

I also changed the bracing layout and re-covered the underside with Second Skin CCF (not completely finished in this photo). The unsupported span (between where the amp rack sits on the enclosure and bracing) is smaller than it looks.

While I was at it, I painted the sub baffle and applied new Second Skin CCF to the underside. Admittedly not the best job on the paint, but it will be covered by a beauty panel. I later figured out that that MDF had to be sealed before its painted. Who knew?

Here are the major changes I made to the layout of the amp rack. I moved the DSP to the "top" so the RCA's could all be routed cleanly down the center. I also cut a small hole in front of the DSP for wire routing and moved the barrier strips for the speaker terminals to allow easier access from the rear seat when setting gains.

While I had everything apart, I decided to TechFlex the wiring. To easily differentiate the power and ground wiring, I used red (with a black stripe) for the power and full black for the ground. I tried using red heat shrink on the power cables, but all I had was the 3:1 adhesive lined stuff, and it was just too thick for JL's crappy plugs. I ended up just using the thin, standard black heat shrink on both positive and ground which worked out fine.

In the very dark photo below, you'll also see one of my modified stinger 6000 directional twisted pair interconnects merged with a stinger 6000 Y adapter. I had to Y every RCA (except the tweeters) because JL's amps don't work with mono RCA's. From JL's manual: "Connection of only one RCA input will result in reduced power output, increased distortion, and could cause the amplifier to overheat. To connect a mono signal to both inputs, use an RCA "Y-Adaptor" (SOLD SEPARATELY)."

 

[Chris12]

Heres the amp rack with everything except RCA's.

I used a numbering system for all the speaker wires and RCA's: #1 = Left tweeter, #2 = Right Tweeter, #3 = Left Mid-Range, etc.
While I can recall this by memory right now, this may not be the case in the future. This being the case, I plan on adding a laminated key card to the amp rack (at some point.) I've seen Bing (simplicity in sound) do this in at least one of his builds.

Along with some of the other changes I made to the amp rack, I switched from using adhesive zip tie anchors to screw down cable clamps. I was very pleased with the end result. I think they look a lot cleaner, and are much more secure.

I also started fabricating the beauty panel for the false floor. Heres what the reveal will look like on the amps:

And, here's where I'm at with the beauty panel.

I haven't decided exactly how I'm going to finish it - I'll either paint it with SEM Landau Black or cover it with black vinyl.

For edge treatment, I bought a Whiteside Router Chamfer bit 2310. I'll need to add material to each opening to get the depth but it'll be nice and deep. Its advertised at 1-1/2" cutting length and 1-1/16" cutting depth.

 

[Whiterabbit]

Any shows going on these days? Bing still hosting shows?