2009 BMW 335i SQ Build Log

[ejeffrey]

I got this car around 2 1/2 years ago to replace my Dinan 540i wagon. I miss that car, but this one is lighter, has a motor that's just as nice, and has a clutch pedal. Add in a Dinan suspension, and it's as close to an ideal daily driver for me as you can get.

I wanted a system that maintained the stock appearance of the car but that also had a bit of flash underneath, and there's a few installs in this forum from the fine folks at Simplicity in Sound that caught my eye. And after hearing the blue F30 that they did, I really didn't have to do a lot of research for what components I wanted. A big thanks to Bing for being a great vendor for all the speakers, and for the system demo.

Equipment list:
- Helix DSP
- Arc Audio XDi 1200.6
- Arc Audio XDi 600.4
- Morel MT-350 tweeters
- Morel Hybrid 4" midrange
- Gladen 8" underseat woofers
- Audiofrog GS10D2

So, spoiler alert, there's not going to be a lot of originality in this install. I don't have the time right now to reinvent the wheel (although I'd like to) and I know the potential. I've got a good amount completed and will be posting some progress updates shortly. This is also on DIYMA, but I want to catch up here.

[ejeffrey]

Here's the start of the enclosure. I've done fiberglass work before but it's been quite a while, and I haven't done this type of enclosure before. I'm also using the big box garbage resin (but this is the last time for that) so it's been a bit of a learning curve.

I did the whole process of taping off the side area and used car wax as a mold release, and protected the rest of the trunk with painter's plastic (steps not pictured), and put down two layers of big box (thin) chopped mat. Lessons learned:
- Use good resin
- Use 1.5oz chopped mat
- Get a roller
- Don't mix the resin as hot when you have to put 'glass on vertical and overhead surfaces
- Pre-cut the mat into shaped pieces and not generic squares
- Take your time on this step

After the initial mold cured, I pulled it out and put on another 5-6 layers of the 1.5oz mat. If you look closely at the last pic you can see places where I didn't get the first layer down all the way at some edges, but these spots were filled with body filler afterwards. If I had to do it again I'd use smaller pieces, or at least stretch the mat before I put it down. By the last layer I had finally started to get the hang of things again. I know the top edge follows an odd profile, but more on that later.

[ejeffrey]

I recently bought a Porter Cable router and a circle jig and this was the perfect time to try them out. Man, sure beats having just a jigsaw. I cut a speaker baffle out of 1/2" MDF, and then two trim rings out of 1/2" and 3/4" and glued them together. I then routered a quarter round on the outside of the trim rings.

Since the sub is pretty heavy, it took a while to get the ring positioned just right. It also helps to use a good glue gun... After that was done I made a bracket out of an old steel bike rack bracket I had laying around. A notch was cut in the enclosure with a Dremel and a small cutting wheel (thanks for letting me borrow it, mom!) and then the bracket was bent on a vice with a hammer and trimmed. Finally, I bolted the bracket in and sealed up everything with silicone. This will be what holds the enclosure to the car on the top, where one of the existing plastic carpet rivets will go through.

With that out of the way, I wrapped fleece around the whole thing. I also learned that you have to really soak fleece with resin otherwise it won't go all the way through. Off came the first piece and on went a new one along with almost a quart of resin, then two layers of fiberglass mat.

After that was allowed to cure, I put a thin layer of body filler on and did a lot of sanding with a belt sander and an orbital to get it trimmed.

When I routered the baffle/trim ring, I accidentally set the bit just a hair below the surface. Not that it would have made made a real difference if it were flush, but it turned out to be a good thing because it left a small step before the round, so when I sanded away the fleece it was easy to see where I should stop sanding.

[ejeffrey]

When I went to test fit the enclosure in the car, I found that the edges had shrunk in almost 1/8" on some sides making it fit pretty loose. Is that common with fleece in general, or is that a result of using poor-quality resin?

A good solution I found was to put a small strip of trunk liner on the edges where it was loose. I'd rather not have to do that, but it actually looked great when I tested it with a piece of trunk liner.

I put on another layer of filler and sanded it down, so now the thread is caught up to my progress. The next steps:
- test the volume with water
- add the sub mounting hardware
- upholster the whole thing
- add the speaker wire.

[ejeffrey]

Installed t-nuts, painted the speaker baffle, and checked the volume of the enclosure with water. The box that Audiofrog suggests is 0.7 cu. ft. gross volume, or about 20 liters. I ended up with 24 liters, so I made a block off plate out of MDF for the top right and sealed it off with silicone. I was also able to fill a couple pin holes at the same time.

[ejeffrey]

Enclosure was then carpeted, and sound deadening and speaker terminals added.

free image hosting site

[BigAl205]

I love that enclosure

[ejeffrey]

For the sub grille, I routered and stacked two pieces of MDF and put a 1/8" round on the top edges. I've never pressed a grill before so I really didn't know how it was going to turn out, but to my surprise it was exactly as I envisioned. Super, super happy with how it came out.

I made a jig from just 1/2" MDF and glued it together, then used the circle jig and the router (absolutely loving these new toys) and made the male/female pieces. 5/16" bolts were more than sufficient for the force required to form the aluminum. If I do another grille like this, I'd say that without a press, 3/4" MDF would probably be better, especially if the press height is anything over 1/4". Putting a 1/8" round on the inside (male) disc ended up working out well, and I think you'd definitely need to do that for press heights over 1/4".

I found that the metal part of the sub grille would rattle the slightest amount when tapped on, so mounted it with some very thin foam which fixed the issue. It's fastened with small nails instead of the preferred staples because the lip is only 1/4" thick, and I didn't want to chance a staple going through or cracking the top.

[ejeffrey]

I spent a considerable amount of time trying to figure out where to put the amps and DSP. There have been a couple family trips where the trunk was literally full, so raising the full floor wasn't something I wanted to do. The rear seat doesn't fold down, but giving up 3-4" on the back wall was a bit too much.

In the end, I settled on putting the DSP and 600.4 under the floor in the space where some BMW processors would normally go, and the 1200.6 where the stock amp is (underneath the subwoofer, more pics on that later).

There's not much in the way of bolts/studs/etc. for an amp baffle to grab on to underneath the floor, so I had to get a bit creative. First, I cut and trimmed two plates to lay flat. Then I made some aluminum tabs that bolt to the plates via t-nuts on the outside edges underneath. These fit into the slots on the sides of the "tray".

I then made a T-shaped holder that bolts to the two studs in the middle of the trays and presses down on the inside edge of each baffle. On each side there's a locating pin that corresponds to a hole in each baffle so everything is properly lined up.

The pieces were then painted black, hardware attached, and bolted in the car.

[ejeffrey]

I made my own signal cables. For the actual wire I used Canare L-4E6S, and the ends are Switchcraft 3502ABAU. Markertek had great prices on both with the added bonus of free shipping, so I was able to get custom cables for about $90. Can't wait to get these things in the car.