So I’ve been meaning to do this write up for quite some time, and since I’ve recently sold my S2K (moved onto a BMW 135i!) I figure it’s better late than never! If you’re interested in purchasing the enclosure check out my FS thread

Audio Partout For sale thread

The goal with this build was to create a custom fiberglass/MDF subwoofer enclosure that would sit in the bottom of the tool well and take up as little space as possible. I had done my research and didn’t want to pay for an enclosure that would take up the entire well, as I needed the space for frequent weekend trips with the wife. I settled on building my own enclosure and decided to use a Pioneer shallow-mount 10” subwoofer (TS-SW2501S4) that requires only a minimal amount of volume (ideal spec for this sub is 0.45 cubic feet, a fraction of what normal 10” subs require). This would be the third enclosure I’ve made and definitely the easiest enclosure I’ve made to date, since the bottom of the tool well dictated the shape of the fiberglass and the top is just MDF and required no funky shapes.

This build was completed over the course of a few months, as graduate school sucked away all my time and money. It was truly a labor of love and I’d spend a few hours every other weekend adding another layer of fiberglass and resin, sanding, trimming, etc., until it was finally complete a few months after I set out to build it. I won’t bog down this thread with a complete write-up on how to fiberglass (as they’re all over this forum and the internet), but I will give a brief overview of the steps involved.

First things first, you’ll need to gather all your supplies and equipment. Here’s a short (and probably incomplete) list of what you’ll need:
• Fiberglass resin – I purchased mine from a local marine supply company. WalMart and auto part stores should carry the 3M/Bondo fiberglass resin but it’s cheaper (and better quality) to get marine-grade fiberglass in a one gallon size rather than buying the Bondo stuff in quarts. 1 gallon is more than you need (I would estimate that I used 2 quarts) but the per unit price is cheaper and I have plenty left over for future projects.
• Fiberglass cloth and chop mat – I used both chop mat and cloth, usually alternating with each layer to add strength. Can be found the same place you purchase your resin.
• Painter’s tape and foil
• ¾” MDF
• Jigsaw/drill – To cut the MDF to size, cut the hole for the subwoofer and mount it
• Dremel w/ cutting wheels – to cut and trim the enclosure to spec. size
• Sanding block and various grit sandpaper – to smooth out any imperfections in the fiberglass and to also rough up the edges of the MDF to enhance it’s bonding to the fiberglass tub.
• Automotive carpet – a local audio shop was kind enough to supply me a square yard of cloth for a few bucks.

Using blue painters tape, I taped up the entire tool well and the outlying areas. Once everything was taped up, I added another layer to really ensure that I wouldn’t get any resin seeping through and bonding to the carpet. I also added a layer of foil on top and taped it down to help release the initial mold. I also went another step further and lightly sprayed the foil with cooking oil before putting down the first layer. I also covered the outlying areas with plastic bags to ensure that it was protected from accidental spills or drops of resin.



For the first layer I used mainly fiberglass cloth, supplemented with bits and pieces of chop mat to ensure full coverage on the areas where it was difficult to lay down the cloth (corners). Once the resin had set and cured, I pulled out the mold and added subsequent layers outside of the car. At this point it’s safe to pull off all the foil and tape from the tool well as you’ll be working outside of the car.


After about 5 layers of alternating cloth and chop, I decided that my enclosure was strong enough, and moved onto trimming it down to size. Determining that it was strong enough was simple enough… I flipped over the fiberglass enclosure and stood on top of it (180lbs). No creaking, cracking, fractures, or breaks… good! The first thing I did before cutting and trimming the enclosure was determining how much volume I would need to get to the ideal spec. for the sub (0.45 cubic feet). I filled up the enclosure with water, liter by liter, and ended up tracing a line around the water level once I had added 13 liters (which corresponds to ~0.45 cubic feet). I then used my dremel and some cutting wheels to cut around that line.


The next thing to do was creating the MDF top and bonding it to the fiberglass tub. I used ¾” MDF and used the piece that sits on top of the foam tool well as my template. I traced the template onto the MDF and retraced (measure twice, cut once!) before taking the jigsaw and cutting it down to the template. I then went on to draw some centering lines and used a compass to draw a circle corresponding to the correct diameter needed to get the subwoofer to fit perfectly. Again, use the jigsaw to cut the hole to size.



The edges and corners of the MDF top was then roughed up with low grit sandpaper and bonded to the fiberglass tub using more fiberglass and resin. At this point I drilled a tiny hole in the tub and forced some 12 gauge speaker wire through, I then plugged the whole with some resin to ensure an air tight seal. Once everything had cured it was sanded down to a uniform and clean finish and spray painted black. Carpet was sourced from a local audio shop (Midwest Audio Visions) and 3M adhesive was purchased at an automotive supply store. This was the first time I had attempted to carpet something and admittedly I did a sub-par job on the sides and bottom of the enclosure. This is a non-issue though as it’s not noticeable.

The subwoofer was then wired up and mounted. I also purchased a speaker grill to protect the subwoofer from anything that I may put in the trunk. Suffice it to say, the subwoofer and enclosure compliment each other perfectly. It hits nice and tight and provides plenty of bass. I wasn’t looking for anything bone-rattling, but desperately needed some low-end fill in the cabin. I got all that and more, as certain songs are definitely capable to some minor bone-rattling! The subwoofer was powered by an Infinity REF1600A amplifier, providing 400W RMS x 1 @ 4ohms. I had the amplifier set at close to 75% so as to not overpower the 300W RMS rating of the subwoofer.



As I no longer have my S, I no longer need this enclosure. It’s sitting in my living room looking for a new home! This is NOT a for sale thread, so don’t post in this thread unless you have questions regarding the build! If you’re interested check out my for sale thread… feel free to ask any questions!
Audio Partout For sale thread

 

A few questions.

Is the MDF portion of your box the same length/width size as the tool cover?

How much higher does the top of the box sit above the original tool well cover?

 

It's approximately the same size as the tool cover just slightly bigger. I can't tell you for certain since I no longer have the car but the tool cover served as the template for the MDF top. With the added fiberglass and carpet, it's a little bit bigger but not by too much.

As far as how much higher it sits than the tool well cover... I'd say no more than an inch. 3/4" MDF + 1/4" (?) of fiberglass and carpet. The top of the fiberglass tub goes to the height that the tool cover goes to, and the MDF adds ~1" to that. Pulling the enclosure out is easy because of the gap between the top of the enclosure and the side of the bottom portion of the well.

Hard to explain so I apologize for that... the bottom half of the tool well (where the foam and cover are) is ~0.5 cubic feet... making it the perfect volume for the sub I used (spec. volume 0.45ft^3)

 

Thanks for the info. From what I understand the height of the completed box is about an inch higher than the stock tool cover.

By the way, I never understood after reading all the tutorials how you seal the MDF top onto the fiberglass box.

 

Yup... sits about an inch higher.

The resin used in fiberglassing is more than strong enough to bond to MDF. I sanded the corners and edges that connected to the fiberglass tub to give the resin a rougher surface to grab onto and bond to.