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2013 Flex - New audio build - detailed how-to's along the way

Started by Lanson, March 10, 2014, 05:12:42 PM

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Lanson

Hi guys/gals,

This build will be full of "How to" info, somewhat in extra detail so everything is laid out so others can reproduce results like this or use them as a starting point.  To audio install experts it will probably seem remedial, whereas for newbies or novices, I might be able to help somewhat.  Just let me know if something needs tweaking to further explain or show something in particular to help


I've been working with a forum member (and now friend) at the Flex forum, on a build.  It first started out with some product and idea discussions, planning, etc.  Then the progression to designing a box (as I've detailed in this thread http://www.ecoboostperformanceforum.com/index.php?topic=2172.0), and then came the discussion of who would install it, and when.  That ended up being him and I over the course of last weekend.  I designed and built the box (as the previous thread mentioned shows) early on, and prepped wiring etc. before his arrival, to save precious install time.

The equipment:

JBL MS8 processor
Vibe UK Slick Stereo 4 amp
Vibe UK Slick Bass 1 amp
Image Dynamics XS-57 5x7 components including the XS28 tweeter
Sundown SD-2 D2 10" subwoofers (pair)
PAC TR-4 remote-on adapter
Sound Deadener Showdown (SDS) deadening supplies
RAAM Audio deadening supplies
T-Spec main circuit breaker, and fused distribution block
1/0 and 4 gauge welding cable
lots of Techflex and heatshrink


This first section will consist of the how-to on the subwoofer box, which was made before the actual install started.

The build began with an idea of making a subwoofer that fits in the spare tire well, but out of wood instead of the typical fiberglass bottom.  I have done many fiberglassing projects but the smell, mess, and cost make working with the stuff very difficult for me.  The spare tire well is actually a geometric shape that is simple to build around.  It took me 3 builds to realize that it is not just a wonky shape, but an actual "perfect" shape.  I'll explain: 

This is the spare tire well, from my 2010 Flex build but the shape is unchanged over the years.  I would bet there are lots of current Ford vehicles with a shape like this.


The shape is easily reproducible, it turns out.  The reproducibility means that building a box that fits inside of it, becomes something not only doable, but EASY.  First, draw a square.  In the case of the bottom of this well, I went with 26" square.  Find center point by drawing an X from corner to corner of the square.  Draw a half circle on one half of the square, so that radius is 13".  For the other half of the square, draw two X's side by side, so these would then be 1/4 of the square, each (x2.)  These get 1/4 circles from the X's drawn, and that turns out to be 6.5" radius.  That's the whole box shape, drawn in seconds.

My reason for explaining this is so you can build one without much effort, because you don't even need to measure your trunk now.  By the way, if you make the square just a little bit smaller (let's say 25"), it would probably fit a little better (lower) in the tire well than the one I did, but would be a smaller box overall.  If you have lots of wood to work with, I suppose you could layer one over the other (say a 25" square and a 27" square), and cut out the shape to make a hollow step.  I didn't have spare boards to cut, so I kept it simple, but you can see the potential here to make this work however you wish. 

This is the shape I ended up with in my design.  By segmenting the shape into straight lines (6 for the half circle and 3 for the 1/4 circles, each),
 

The angles for these cuts turns out to be very predictable.  Since each 1/4 circle needs 90 degrees to make the angle, we simply divide that by 3 (per 1/4 circle) and we get 30 degrees.  That turns out to be 15 degrees per side of wood, and that's what the saw is set to.  For straight sections, they received a 7.5 degree cut (1/2 of 15 degrees.) 

There's some metal that serves as the spare wheel mount in the center of the well, so you'll see that the box I made has some cutouts to handle that.  All I did there was measure distances and cut bit by bit into the box, until it fit into place easily.  I do believe my saw was off about a degree, because in the end my cuts were not "perfect", but still workable.  Here's some in-progress pics.



So after the test fit was successful, I glued and air-nailed the box together, one section at a time.  Then test-fit again to be sure.  You can see here that the cutout has been covered with a layer of wood.  Not shown but part of this design, I had to rout a roundover into the box's bottom, which let the box sit in the well just a bit better.  The box's sides have a height of 4 7/16".  This could be a variable number that could go higher for deeper subs (at the expense of not having the seats fold flat), or lower with more shallow subs (and the seats could then lock flat.)


This is a sneak peek test-fit of the Sundown sub in its new home.  The top of the box is not actually installed here, just three brad nails to hold it in position so I can cut my circles.  I use a Jasper circle jig btw.


These are a few test-fit runs, to find out the final height of the installed system.  We are using bar grilles on the subs to give them the clearance they need while still protecting them from the seats.  This will be augmented with an additional cover as well.  As you can see, the seats will still flip and fold almost flat, but not quite.  This was considered an acceptable thing by the recipient of this box, but if 




Now the box top is glued and nailed together, and set into place with clamps overnight.  I've also sprayed the interior with a high quality rubberized sound deadener/sealant I found from Rustoleum. 


The next day, I started on the box's cosmetics.  I chose a vinyl that matches the upper section of the interior in a Flex, followed with a durable black "trunk liner" grade of carpet on half of it.  The separation of the two will become apparent in a bit.  Also note the banana plug terminal installed.  In case you are new to installing, buy air tools and the appropriate air compressor and accessories.  I use an inexpensive but pretty well made air nailer/stapler from Walmart of all things.  Staples are great for low-depth things like this vinyl, and nails are fantastic for box building in general, but staples can work well too (with glue.)  Once I finally made the jump from screws and glue to air (and glue), my box building speed tripled.  I can discuss this in more detail in another post if anybody is on the fence about going with air tools.



This is a close-up of the sub we're using.  Note the side vents, especially.  This sub has no back pole vent, and that means the sub can sit in a box that is no deeper than the sub is itself.  This is a big advantage with a build like the one we're doing here.  Not many subs have this feature, and most you must leave some space behind to let them breathe properly.  This is a dual voice coil sub, 2 ohms each on this model.


I built a simple spacer board and wrapped it in vinyl as well, then test-installed the box.  Turns out, it is very (very) heavy, and it barely fits.  The shape ends up being a bit of contortion to get in, and out of the trunk.  I wouldn't build a box any taller, or longer than the one I'm sharing with you here, because it most likely will NOT go in the car once you've built it. 


These test fits are in my own Flex, and you'll notice that my back panel is cut to allow the box to fit.  This is pretty much the only permanent "mod" you must make to your car, for this type of box.  This panel isn't nearly as expensive as others on the car, should you wish to return the vehicle completely back to stock. 


This is a further test-fit of the intended top cover board.  Note the green LED which may or may not make it in the final rendition, but was fun to play with.  I'd like to give you more details as to how I made this top cover, but really it was a lot of trial and error.  Once I had the subs in the box, and the box in my Flex (as a test), I found myself with a problem.  That problem was, how do I make the top cover fit right?  So I drew up a template and cut a shape which worked, but then the issue of cutting out the subwoofer hole came up.  I ended up making tiny cuts first, and I measured where I was vs. where I wanted to be, and inched myself through with cut after cut, until the board plopped into position perfectly.  I actually made one board and completely mis-cut first, then did it all over again (correctly this time), with a new board.  Sometimes you just have to learn the hard way.


After I got my shape, beveled/smoothed the edges all around and sanded it, then wrapped it with some plush carpet to get it looking nice. 


You can probably see why I made 1/2 the box top with black carpet now


This is how the shape of the board fits against the back panel, excuse the saw dust.


The board actually sits right in line with the grille, so objects can be placed on the carpet and grille as one.  I'll probably make a final cover board for both, later.



Continued with more (much more) later on...
I don't have an EB but I am an avid modder and happy to help the community and learn/grow.  Pretty good with audio and wheels, my build and discussion threads are here in the forum.  2013 Flex AWD N/A

Audio:  Dayton Reference home speakers in front stage, incl. 2-way passive custom pillars 2.5" mid, 3/4" tweet, 2-way passive custom center channel 5" mid, 3/4" tweet, 8" midbass in doors, Vibe UK amps, JBL MS8 processor, Optima Yellow-top custom-wired, Exile subs in spare tire well

Mods: H&R, K&N, 22x9 & 22x10 3 piece forged wheels 265/35-22 Toyos, SCTX4 w/ 91 oct. Torrie tune

BiGMaC

Lansom... Excellent write-up!  Great explanations.  I can hardly wait for more

...and I owe you some SHO trunk measurements I think.

Great work... Thanks for sharing it!

•2013 Taurus SHO nonPP - All Ford factory options, 3BAR MAP, LMS v8 tune (mods for 3BAR, DPs, and T-stat), Paint & plastic correction, CQuart finest all exterior surfaces, limo black window tint,VLED Triton switchbacks, Daytime BrightLites switchback DRLs, full interior and exterior LED conversion, Lamin-X charcoal blackout tail lights and reflectors, PPE catted and coated downpipes, EBPP coated hotpipes with BoVs VTA, MDesign CAI
•2013 F250 CC Lariat 6.7EB Diesel -stock

Lanson

The next part of the build involves the actual car, and we did our best to document all we did, for purposes of helping others trying to follow along.  Sometimes, the camera was just not within reach, so I'll document some parts just in text. 

This is Stefan's Flex.  We started by pulling the cowl to gain access to run our power wire from the engine bay to the cabin.  The wipers are the first to go, and to remove them, we pulled the caps off the tops of the wiper arm, and removed the 15mm bolt.  The wiper shaft is splined, so the wipers will not come off without some serious effort.  to provide that effort, we used vice grips with thick towels to keep the teeth from digging into the coating on the wiper arms, but did manage to nick them a little bit.  The idea is to use one half on the backside of the arm, and the other half on the top of the wiper shaft, and try to close the gap, thereby popping off the arm.  I bet a "puller" tool of some sort, like a gear puller, might be a good option.  They were "very stuck", but eventually came off.  No pics of this part, as we were frustrated just trying to get it done.  What you see here is us starting in, after those suckers came off.


Next we pulled the cowling from the windshield, with just some pressure by hand in a pulling motion.  Came right off.  There are simple clips along the length of it.



There's these edges of the cowling that simply lift up and away from the main section.  A few tabs keep them in place.


On the engine bay-side, we pulled the fastener clips that hold the cowling.  A small flat screwdriver was sufficient to lift the center of the clip which holds the pressure.  Don't lose them in the engine!  Also, don't forget that the passenger side has a small tube which is the wiper washer fluid tube.  Just tug and it will separate at its connection.


The top of the cowling is off, and this exposes the lower portion.  It is made of two segments that overlap.  They remove with ease, just pull the couple metal clips that hold it to the metal of the engine bay, and then pull a few tabs.  Again, don't lose them in the engine.

http://im1.shutterfly.com/media/47a4dd29b3127ccef5c489e617f600000030O00AcOWjRo1btGQPbz4C/cC/f%3D0/ls%3D00204754449820140309054848114.JPG/ps%3D50/r%3D0/rx%3D720/ry%3D480/

The PCM is hidden in here




We're getting a first look at the intended reason for pulling the cowling.  Over by the driver's side is a very large rubber grommet.


There it is!  This is THE fastest way into the cabin that I've found.  I didn't discover this until my 2nd Flex, and for my first one I poked a hole right through the firewall by the brake pedal.  Trust me, just use this way.


Stefan wanted to do some inventory shots




Continued...


I don't have an EB but I am an avid modder and happy to help the community and learn/grow.  Pretty good with audio and wheels, my build and discussion threads are here in the forum.  2013 Flex AWD N/A

Audio:  Dayton Reference home speakers in front stage, incl. 2-way passive custom pillars 2.5" mid, 3/4" tweet, 2-way passive custom center channel 5" mid, 3/4" tweet, 8" midbass in doors, Vibe UK amps, JBL MS8 processor, Optima Yellow-top custom-wired, Exile subs in spare tire well

Mods: H&R, K&N, 22x9 & 22x10 3 piece forged wheels 265/35-22 Toyos, SCTX4 w/ 91 oct. Torrie tune

BiGMaC

Looking good!, Great info!...  :thumb: I'm anxious to see the next installment!

•2013 Taurus SHO nonPP - All Ford factory options, 3BAR MAP, LMS v8 tune (mods for 3BAR, DPs, and T-stat), Paint & plastic correction, CQuart finest all exterior surfaces, limo black window tint,VLED Triton switchbacks, Daytime BrightLites switchback DRLs, full interior and exterior LED conversion, Lamin-X charcoal blackout tail lights and reflectors, PPE catted and coated downpipes, EBPP coated hotpipes with BoVs VTA, MDesign CAI
•2013 F250 CC Lariat 6.7EB Diesel -stock

Lanson

Right about now, I would usually show you how to drill through this false metal firewall by the wire loom here, to make a safe entry to the grommet.  HOWEVER, Stefan and I came across a better way, and I'd like to share that with you.  Turns out, there's a drain/grommet type rubber thing down at the bottom of this area. 

This shot hints at how this will work, but basically if you look down just forward of the large cabin wire loom grommet, you'll find a racetrack-shaped rubber grommet that serves as a drain for this area of the cowl.  I pushed wire through that grommet, and this actually works as a safe entry point for wire to the cabin grommet.






Just cut a small slit in the large rubber cabin grommet.  Use a very sharp, stubby blade, carefully so as not to damage the wiring already present.  Then push your wire right through.

I took a lot of pictures of the entry point of this wire, but they were all either blurry or pitch-black.  Basically, it is very hard to photograph exactly what you need to see under the dash, so I'll describe it.  If you look up underneath the dash on the driver's side, you'll see a circular hole at the corner to the left of the pedals and up.  In that cutout circle will be the wire poking through, just pull it slowly into the cabin. 

We then started on the interior.  Pulling panels in the Flex is pretty easy as is most Fords, just be careful and use a panel popper or a plastic pry tool when necessary.  We started with doors, which come off with nothing more than some screws around the perimeter, a pick tool to take out the hide panels by the handles, and a 10mm socket for two bolts.  Just remove those, and then pull directly, don't lift (yet).  The door will actually come straight off just enough to let you disconnect the connectors, and for the door handle itself, just pinch the small plastic tabs that hold it to the door skin, and remove from the door and let it hang.  Sorry for no pics here, doing this door is so automatic for me I had it off in seconds.

This is what you have when the door skin is off and the vapor barrier plastic removed.  Stefan was hammering on this part of the car, while I was in the trunk.  To keep things congruous, I'm going to focus on the door stuff first, then show you the trunk.



He's laying on the deadening, first using Don's Sound Deadener Showdown (SDS) tiles.  These are heavy-duty, and you want to make very sure you are using gloves.  These can cut you in ways that no other product I've used can, because they use a thick metal top layer. 




Now he's using RAAM Audio's RAAMmat product in layers in and outside of the door.


We noticed that the Ford dealer installed some sort of alarm and poked a hole through the door wire grommet.  This, while not being my favorite way to install speaker wire, looked as good as any option, given the size of wire we were using and the extreme shape of the grommet.  My wire followed that path
This was the dealer wire already in the car

I added my wire


The dealer hacked this inside panel a bit, with wire haphazardly installed on the outside of the panel


I drilled a hole instead for mine


These are the Image Dynamics connectors that come with the kit, which are slightly larger than the stuff I usually have in my stock of materials.  The different colors on the connectors indicate different size widths.  Note the Ensolite foam I added around the speaker, to form a gasket.



Speaker is in


Door is getting finished.  Stefan is using a layering technique with deadener to fully seal the door, this is a really good option for our gaping holes that must still maintain that indented shape (to fit the door skin.)  Otherwise, covering with metal or some other material would be a suitable way to go.  This way though, is extremely effective in killing sound and sealing the door up and I like it.



I covered the door in Ensolite, and added a layer of foam rolled around the speaker to serve as a gasket between the door skin and the speaker. 




The door skin also got the same treatment in deadener, and I put some Ensolite around the speaker opening too.


Perfect!  Note that for those willing to experiment and perhaps cut some factory stuff, I think a 6x9 would fit here.  Maybe.



I don't have an EB but I am an avid modder and happy to help the community and learn/grow.  Pretty good with audio and wheels, my build and discussion threads are here in the forum.  2013 Flex AWD N/A

Audio:  Dayton Reference home speakers in front stage, incl. 2-way passive custom pillars 2.5" mid, 3/4" tweet, 2-way passive custom center channel 5" mid, 3/4" tweet, 8" midbass in doors, Vibe UK amps, JBL MS8 processor, Optima Yellow-top custom-wired, Exile subs in spare tire well

Mods: H&R, K&N, 22x9 & 22x10 3 piece forged wheels 265/35-22 Toyos, SCTX4 w/ 91 oct. Torrie tune

SHOdded

Great info for the ever-bewildered Flex audio/video modder :)  Not having to drill the firewall is a PLUS.
2007 Ford Edge SEL, Powerstop F/R Brake Kit, TXT LED 6000K Lo & Hi Beams, W16W LED Reverse Bulbs, 3BSpec 2.5w Map Lights, 5W Cree rear dome lights, 5W Cree cargo light, DTBL LED Taillights

If tuned:  Take note of the strategy code as you return to stock (including 3 bar MAP to 2 bar MAP) -> take car in & get it serviced -> check strategy code when you get car back -> have tuner update your tune if the strategy code has changed -> reload tune -> ENJOY!

Lanson

Now I'm going to double-back, and show you what I was working on when Stefan was doing the door deadening.

I started by laying down SDS tiles like we put in the door, in strategic spots. 


I then layered RAAMmat on top




I then started on the ground we'll be using for the system.  I elected to use the passenger seat's LF seat bolt, like I've done before with the Flex.  Safe, strong, and noise-free.  This is the location


This is after a couple minutes with an air grinder (God I love air tools)


The bottom of the seat got the same treatment



This is the ground I made.  I formed it from a 1/0 gauge ring terminal that I shoved two 4 gauge and one 8 gauge wire into, then crimped, then pounded flat with a mallet.  Then I covered it with techflex and heatshrink like we've done with the rest of the project.



I also prepped the amps for the passenger seat area, and ran a subwoofer speaker wire to the trunk




We then went to tackle the circuit breaker mounting, and opted for the fuse box itself.  We secured it with nuts and bolts directly to the top of the box.


And connected the other side with a 1/0 ring terminal directly to the factory battery and terminal. 



Top cover still closes, just had to trim the cover a little bit for clearance.


Here it is, in a completed state.  Detail oriented folks will notice the circuit breaker is flipped to the ON position here.  This pic is actually from one of the very last moments of the build, when we gave the system life.




I don't have an EB but I am an avid modder and happy to help the community and learn/grow.  Pretty good with audio and wheels, my build and discussion threads are here in the forum.  2013 Flex AWD N/A

Audio:  Dayton Reference home speakers in front stage, incl. 2-way passive custom pillars 2.5" mid, 3/4" tweet, 2-way passive custom center channel 5" mid, 3/4" tweet, 8" midbass in doors, Vibe UK amps, JBL MS8 processor, Optima Yellow-top custom-wired, Exile subs in spare tire well

Mods: H&R, K&N, 22x9 & 22x10 3 piece forged wheels 265/35-22 Toyos, SCTX4 w/ 91 oct. Torrie tune

Lanson

So the end of Day 1 finished like this with the pre-wiring of the MS8 to the factory head unit.  The connector disconnects from the head unit without requiring the actual head unit to be touched.  This is good, because ripping into the center console and dash is not fun at all on this car.  So, I reached up into the center stack from underneath, and plucked the connector out of the back of the head unit.  I recommend disconnecting the other one to the left (as viewed from behind the head unit), because the connecting cable of both are connected as one.  With both disconnected, the cable is long enough to work on.


Now, I'm going to step back and show you what I've worked on for days prior, which are the MS8 wiring harnesses. 


So for review of what you're seeing, I'm going to detail what these harnesses do. 

Input - from the head unit, the MS8 inputs LF, RF, LR, RR, and Center channel which is 5 out of 8 possible.  I chose to run all these to the MS8 and let the processor inside it sum the signal into a digital stream.  I debated going with just the fronts, or just the left and right front, but because I don't know exactly what the head unit on this car does for its surround mode and there is no defeat for it, I kept it safe and ran all the channels of input.  To do this correctly, I soldered and used heatshrink on each input, and extended the runs with extra speaker wire.  If you're wondering how much soldering that is so far, that is 10 connections on the input side.  The rest of the inputs are closed off with heat shrink on the ends.


Output - from the MS8, we have 8 outputs.  These outputs can be either in the form of RCA outs so amps can use them, or in the form of speaker outs for a direct connection.  The MS8 has 20W of available power per channel if the RCA out is not utilized.  For our setup here, the 4ch amp is responsible for LF tweeter, RF tweeter, LF woofer, and RF woofer.  The sub amp is of course, for the subs.  The remaining center, LR, and RR speakers are powered off the MS8 directly.  For this harness, I extended it with speaker wire, and there is a direct reconnection to the factory harness for the LR and RR speakers.  The center channel gets a direct run of speaker wire though.  6 more connections soldered for a total of 16 now.

Here's what that looks like in action, as I techflexed the harness and then broke up the various runs into color codes. 



Stefan started on the passenger door. 





Clippin' and solderin' (30 connections now)






Tucking it back into factory position, back in the head unit



We packed it up for the night after that.  I'll detail the rest for you later on as we continue!

I don't have an EB but I am an avid modder and happy to help the community and learn/grow.  Pretty good with audio and wheels, my build and discussion threads are here in the forum.  2013 Flex AWD N/A

Audio:  Dayton Reference home speakers in front stage, incl. 2-way passive custom pillars 2.5" mid, 3/4" tweet, 2-way passive custom center channel 5" mid, 3/4" tweet, 8" midbass in doors, Vibe UK amps, JBL MS8 processor, Optima Yellow-top custom-wired, Exile subs in spare tire well

Mods: H&R, K&N, 22x9 & 22x10 3 piece forged wheels 265/35-22 Toyos, SCTX4 w/ 91 oct. Torrie tune

Lanson

So first thing next morning, we started back at it.  I started working on the A-pillars while Stefan worked toward finishing the right door deadening process.  Here's the A-pillars




This is slightly out of order with the build but since we're talking A-pillars, look what Stefan is doing!  He's taking a 2" hole saw to his pillars, to install the massive Image Dynamics XS28 tweeters.  Precision is required, challenge accepted!







I soldered those up, and got them installed right away



See what I mean about precision required?  Look how close that was to the dash in these finished pics



We then tackled the passenger door wiring and final deadening



Same as the other side, but since it wasn't molested by the dealer, the job went quicker and done better



Dead door!






While I was finishing up the passenger door Ensolite and re-hanging it, Stefan jumped on the tailgate panel




I don't have an EB but I am an avid modder and happy to help the community and learn/grow.  Pretty good with audio and wheels, my build and discussion threads are here in the forum.  2013 Flex AWD N/A

Audio:  Dayton Reference home speakers in front stage, incl. 2-way passive custom pillars 2.5" mid, 3/4" tweet, 2-way passive custom center channel 5" mid, 3/4" tweet, 8" midbass in doors, Vibe UK amps, JBL MS8 processor, Optima Yellow-top custom-wired, Exile subs in spare tire well

Mods: H&R, K&N, 22x9 & 22x10 3 piece forged wheels 265/35-22 Toyos, SCTX4 w/ 91 oct. Torrie tune

Lanson

Let's get back to it.  This is how I like to mount things under the seat.  I take a board, wrap one side in Ensolite, and the other with a layer of butyl caulking rope.  This then goes under the carpet, with the butyl face-down on the metal floor board.  It sticks like glue but is not permanent, does not cure, and will not ruin anything.  Then the amps or processor can be securely installed on top of the carpet.



Next up for me, is the center channel.  I fished up my wiring and installed



Working on the amps








This is the compact fused distribution block we're using.  This will be on the driver's side, by the MS8



From here, the system was live.  I can write up a separate section for tuning the MS8 and such, but that's probably for later.  Here's the final pics of the trunk




I don't have an EB but I am an avid modder and happy to help the community and learn/grow.  Pretty good with audio and wheels, my build and discussion threads are here in the forum.  2013 Flex AWD N/A

Audio:  Dayton Reference home speakers in front stage, incl. 2-way passive custom pillars 2.5" mid, 3/4" tweet, 2-way passive custom center channel 5" mid, 3/4" tweet, 8" midbass in doors, Vibe UK amps, JBL MS8 processor, Optima Yellow-top custom-wired, Exile subs in spare tire well

Mods: H&R, K&N, 22x9 & 22x10 3 piece forged wheels 265/35-22 Toyos, SCTX4 w/ 91 oct. Torrie tune

Torsen

Wow, that sub box is awesome! You have inspired me to try to build a box that fits my spare tire well. Do you find that you get better bass response with the subs facing upward than you would with them firing downward?

Lanson

Quote from: Torsen on September 30, 2014, 12:00:58 AM
Wow, that sub box is awesome! You have inspired me to try to build a box that fits my spare tire well. Do you find that you get better bass response with the subs facing upward than you would with them firing downward?

In the case of this design, you need as much air space as you can get.  Up-firing does that here.  Acoustically, there's little to no cancellation with the subwoofer firing from the spare tire well, so I say acoustically upfiring is good here. 

Also, maybe I'm missing the downfire idea you're thinking of, do you mean the subwoofer inverted, or do you mean a design that has some room where the sub is facing down, and has some air space under it for output?  If that were the case it would probably work, but extra space would be taken to accommodate that so the box would have to be smaller.  Not good!
I don't have an EB but I am an avid modder and happy to help the community and learn/grow.  Pretty good with audio and wheels, my build and discussion threads are here in the forum.  2013 Flex AWD N/A

Audio:  Dayton Reference home speakers in front stage, incl. 2-way passive custom pillars 2.5" mid, 3/4" tweet, 2-way passive custom center channel 5" mid, 3/4" tweet, 8" midbass in doors, Vibe UK amps, JBL MS8 processor, Optima Yellow-top custom-wired, Exile subs in spare tire well

Mods: H&R, K&N, 22x9 & 22x10 3 piece forged wheels 265/35-22 Toyos, SCTX4 w/ 91 oct. Torrie tune