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e86 M Coupe and e85 with premium - Sub add on (56k WARNING!)

18487 Views 55 Replies 26 Participants Last post by  wrh3
Hey there everyone!

First of all - thanks to the many of you have helped me along in this process. As promised, here is a full write-up of my sub installation into my 2007 E86 M Coupe. Although technically this should work with the E85 as well, YMMV. All the wires should be the same for all E85/86 but please double check through BMW WDS if possible before committing to anything other than an e86 M Coupe.

Before we begin, this is a documentation of what I did. Legal disclaimer - these are not instructions and re not meant to substitute for professional installation. By using any of this information you agree to hold me harmless for any issues that may arise. Ok, that out of the way...

First the specifics...

I bought and installed the following gear:

JL Audio 250/1 Amplifier


JL Audio 10W3v3-2 Sub Speaker

The ideal spec for the box for the speaker I selected is .63 cubic feet. I ran some calculations and after all the math of the volume of the sub itself subtracted out, the plans attached here set it at that ideal .63 cubic feet! As a nice bonus to us Coupe owners, the sub fits perfectly into the nifty little shelf BMW made for it next to the battery cover.

Next, the key details for those that just want to jump in:

Initially received some info that turned out to be incorrect. After combing various sites, and ultimately with the assistance of a great guy from Belgium - GV (from z4um - BIG THANKS!) everything is squared away. Here we go:

Power - Direct from battery distribution block (see pic 15)
Ground - located within 15" from amp by scraping paint off to bare metal (see pic 18)
Amp Power Turn-on/Remote - thicker white wire, located in main amp cable bundle (tapped at yellow circle, pic 21)
Right Sound + Amp connector pin 23, blue with white stripe wire, heavier gauge (~18 ga)
Right Sound - Amp connector pin 22, blue with brown stripe wire, heavier gauge (~18 ga)
Left Sound + Amp connector pin 4, red with yellow stripe wire, heavier gauge (~18 ga)
Left Sound - Amp connector pin 3, red with brown stripe wire, heavier gauge (~18 ga)

* the heavier gauge note above is in comparison to the other harness wires. Most look about 24 gauge, but these are definitely easy to spot from the bundle. Also, I was given 3/4 and 23/24 - but my BMW WDS shows 22/23 - in any case, the colors are DEFINITELY correct, as they're hooked up. Pin's don't matter, because they're near impossible to see anyhow.

On to the install!

The pics are all below, but the narrative is as follows:

0 - all construction is done with 3/4" MDF, gorilla glue between butt joints, where two MDF boards touched on the faces, I used contact cement to get them to bond. Everything was then screwed using 2" coarse thread drywall screws.

Before starting on step 01 - I cut all the pieces as identified in my cut list (attached in PDF). I made some field mods, btw, but there is no reason you can't follow as it is shown for more crazy strength. For example, I skipped the right 'A' panel and added an extra E foot. The reason for these doubled up pieces (the ones at ab and cd) are that's where the speaker and amp get mounted. I wanted a solid underpinning. The rest are just for symmetry.

01 - First step , assemble sides b and f to make a perimeter box

02 - Glue with your favorite glue (I like Gorrila glue - as it expands to fill voids) and screw. I used a screw every 3-4 inches. MAKE SURE you pre-drill and countersink the screws. The pre-drilling is not an option - you'll bust the MDF if you don't. The countersink just makes it look nicer, the carpet will lump if you don't over each screw.

03 - Carefully trim and glue the top D panel and the bottom D panel. These go flush. Screw from the sides.

04 - build and clamp the base and feet - the base is c and e pieces. The E pieces are contact cemented together and then screwed (yes yes, I'm sure you're already thinking this... the only two things to survive a nuclear war, roaches and this sub box - they can live in it!)

05 -put box onto the platform, contact cement the two together and screw a few to hold together for now.

06 - mark the center (here you can see my 'few' screws - lol). These markings will be used to cut the speaker hole. Do cut the hole now. As you can see in the next frame, I added the additional A panel for amp mounting ane feet before the painting.

07-08 I painted the parts that would be exposed, could be exposed or could benefit from a hit of black with some flat black paint. (not that it mattered on the rear - I ran out of carpet!

09 - this is where a lot happened without pix. Basically I contact cemented audio carpet to the box, soldered leads to a terminal cup and reinforced it by gluing it with gorilla glue and using reinforcing MDF. The terminal cup was very flimsy and I didn't want it to flex with the bass waves. Here I also mounted the hooks from industrial Velcro on both feet. These are key - with this, the box needs almost no additional reinforcing.

10 - here you can see my crappy carpet shortage. This was the first time I learned that it's not like wrapping presents. Oh well - no one looks there. You can also see the gorilla glue leaking out of the terminal cup. This is on purpose to seal the cup area. Remember - sealed enclosure, means sealed!

11 - In all my research I've read that by using polyfill (dacron) stuffing in the box increases the bass depth. I can't tell if it did - I only did it one way. But since a 10" is the max I can fit - I'll take all the bass lows I can get. The recommended ratio is about 12 ozs per 1 cu ft in a solid enclosure. Since this one is about 3/4 of a foot - I used just a little less than the full 8 oz package (shown behind). BTW: I got this at a sewing store.

12 - This shows how the poly fills the space, but more importantly please note the JL gasket supplied with the speaker. It is critical this be laid carefully so it not bend or rip.

13 - The finished bottom.

14 - Open arse surgery begins. I'm 6' 4" tall and mostly torso, so it was a total biatch working back there. I took a skateboard ramp thing from my kids to be able to kneel 12" off the ground, and leaned over the trunk the whole time. My chest still hurts! Bring pillows! In this pic, you can see the Dice ipod adapter. It's ok - but it was cheap and easy to install.

15 - Here you can see my power leads hooked up to the battery distribution box. It is located between the battery and the exterior of the car in a covered box. There are channels in there designed to add additional cables, but I didn't have the right sized eyelet, so I paralleled an existing cable. Still, it's very clean, doesn't have to hang off the battery + post, because it's off to the side, it's part of the emergency disconnect and more. You can see the main amp fuse mounted to the rear of the battery itself. The positive cables run over the top of the rear firewall, I did this to keep the thick power cable away from the signal wires which run at the bottom of the firewall.

16 - another angle on the battery distro - cover is on now on the distribution panel

17 - mounting the fuse holder onto the supply cable - here is another angle showing the power wire running high

18 - make sure you SCRAPE ALL the paint, ALL the primer and then scrape the bare metal some more. This is where I drilled and mounted a screw and terminal for the ground cable. - note the DICE adapter for bearings.

19 - take two RCA cables, strip their ends, use splice connectors to add them to...

20 - the main wiring harness showing the connections. Please note - this is the way I did it first. THIS WAS NOT GOOD! See next pic...

21 - First I mounted close to the cable, but the second time (when I was given the right wires to use) I moved it to the yellow circle area. I also spread them out so as not to create a lumpy cable.

22 - see lumpy cable? This is why I moved from the red circle to the yellow. The angle that the harness bends made it a royal pain to put in this way.

23 - The cables are routed out as thus. Power is separate from signal all the way until we get to the amp.

24 - last shot before the box shows

25 - In the 24 pic and here you will start seeing a black bracket. It is an L bracket I painted matte black and mounted to the Satellite receiver bracket on the firewall. There is no way to measure it or replicate it - I had an L sitting around that I used. So just find a similar way to do this. It will keep the top of the box from tipping under acceleration. The velcro holds it overall - this is just stability.

26 - another angle

27 - cover comes on for the battery

28 - close-up of the amp area. Make sure you mount the amp in the fins up direction for optimal cooling!

29 - all finished 1

30 - all finished 2

31 - all finished closed, ambient lighting

32 - all finished closed, flash lighting

One key note - the carpet is a perfect match in reality. The issue is that the grade of carpet BMW uses is about 3-4 notches above this one. The nap is thicker and smoother (for lack of a better terminology). The color though, is dead on in reality.

So that's it. I have one more step to this crazy upgrade project. I am putting in MB Quart tweeters in the sail panels. I have no idea if these will work as a replacement as I don't have any resistance stats on the stockers. But If that goes, I'll document it while I go along and add a new thread as well.

The sound? Well - let's say it's the way it should have been. You just can't beat having all that moving air. It was worth all the hassle and headache. And as a bonus - for winter and wet driving... I just put about 60lbs over my rear wheels! If I want to go do a track day, it's 5 minutes... remove battery cover, disconnect main fuse, undo the two main screws on top of the sub holding it in place, disconnect wires and pull it out.

Ok, now going to soak my hands after all this typing. I spent weeks searching for just this sort of info. In the spirit of forums I hope it helps all of you a fraction of as much fun as I had doing it!


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Pix 1-12


Pix 13-24


Pix 25-32

and GIF of plans and PDF of plans.


I also forgot to add.. my original project was going to enclose the entire battery and sub as one unit. The issue, however, is that this needs to be done with fiberglass. As I don't have the means to work on that at this time, MDF had to be it.

The rear area of the coupe is a mess of angles, not two parallel. Best example - the litlte shelf that serves as the support/stand for the unit - it's a different dept across the entire unit. It's only a change of about .75" but - that's more than 0 - making MDF work a giant PITA.

Many thanks for the fantastic post. I've also wanted to improve on the disappointing premium sound system ever since I first listened to it, so I'll have to digest your writeup and figure out what can be done while sacrificing a minimum of trunk space. It might end up being a smaller box combined with palantirion's battery and trunk mods.
Great writeup on an excellent woofer enclosure! :thumbup:

For those that care about trunk space, you could easily get away with an 8" sub and therefore a smaller enclosure. In fact, you could elongate the enclosure (wider instead of taller) to make it be a small shelf against the back seat.

I have a JL 8w0 (8") sub in rear console of my roadster, and it is far more powerful than my ears could handle. I know it doesn't reach the quite as low in the frequency spectrum as the 10w0's, but then again I don't " roll up with my glock out, if you know what I mean dawg"
Thanks for the kind words folks!

Wildag - you're absolutely right. I'm wasting about 3" of height on the feet to have a downward firing sub. I did this because I didn't want to a) see the speaker for theft reasons and b) to not have anything pierce it (sure I could have gone with a screen cover - but they're less than pretty).

So right off, lop off 3" and you're at around 10" tall. Widen the enclosure to the full width that's allowable without changing anything else - and you can drop down another 3 or so inches in height.

Plus - going with different speaker drivers will require different volumes - I'm sure there are other drivers, even in the 10" class that can be done in a smaller enclosure! BTW: the 10W3 drives like a high-end Jazz speaker, not a gangsta - so to some even this won't be enough.

Lastly BKH - the battery mod and this sort of thing are likely to be mutually exclusive. You see high-end amps draw a ton of current which means that little battery may never recharge. In fact, in higher end installations the current supply cannot keep up with demand from the amp - hence people put in capacitors. It would take some calculating to figure it out, but keep that in mind!

Right you are - didn't have my thinking cap on - but then again it was about 2:00am when I posted...:doh:
Lastly BKH - the battery mod and this sort of thing are likely to be mutually exclusive. You see high-end amps draw a ton of current which means that little battery may never recharge. In fact, in higher end installations the current supply cannot keep up with demand from the amp - hence people put in capacitors. It would take some calculating to figure it out, but keep that in mind!
That is one hell of a good right up. Very nice and clean.
Although I've used a/d/s. MB Quart and Rainbow speakers in the recent past, these are the speakers I'd like to see replace all of them if they're a good match and fit:
Oh yea.

Focal = tasty.

I've had a/d/s and quarts as well. They're pretty good. I've also had some Dynaudio stuff that was out of this world. But, alas, this is just a sound reinforcement project - it's a leased car and no sense in going over the top - famous last words mind you!


peeti, Im thinking about doing this in the next month or two... are you still as happy as you were when you installed this stuff? Also it looks like the amp is wired in with a full range of sound Ive got a 5 channel amp so if it does have full sound range I could easily replace the other speakers in the car (If I so choose... )
hella ya. Especially now that I can open the windows to sweep out the standing waves. Very happy. In fact, I find myself driving around with the EQ on screen - it's annoying that some of my eclectic collection is flat and some super bassy!

I ran full spectrum in and set the crossover on the eq amp to cut below 100. I also shut out infrasonics to protect the speaker - but that's specific to the amp itself.

I cannot confirm that I am receiving a full range - but I believe that to be the case. If that's so - you should be golden. However - you will want to seek out the rear wires as well so you can do fades!!

Good luck!
Hey Peeti, Great write up! I was wondering are the original subs still connected and being used also or just the new sub? I wasn't sure if you tapped into the signal wire or cut the wire. Thanks
thanks for the info! now i REALLY want to build one... Ive got most of the pieces, but I must make myself wait until after we decide if were going to buy a new house or not....
Great write-up mate! Looks sweet.
Looks great! I like the location because I tend to find those "awkward" shaped spaces in the trunk are useless anyway. Might as well fill it up. I did a similar amps-to-box mount in a VW I used to have.

My M3 had Focal Polykevlar separates.. very very sweet speakers, I preferred them to the MB Quarts I had in my VW.
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