Kurt's 2001 Z3 3.0 Roadster

My Z3 is 2001 3.0 model that came with BMW's top of the line Harmon Kardon (HK) stereo system. The HK employs a dual speaker subwoofer box which is housed in a compartment between and behind the seats. The Roadster Sound enclosure is designed to fit in the same space.

First of all, I am in no way a professional stereo installer. In fact, this install was the very first time I had ever installed an amplifier (two, in fact) and subwoofer into a car. I can use basic hand and power tools and can follow instructions, however. I also appreciate reading online about how others have "gone before me" which removes some of the mystery from projects like this one. I feel that nearly any Z3 owner can be successful in upgrading the subwoofer capability in their car with the unit from Roadster Sound.

I had long ago removed the stock HK unit in its entirety (the two trunk mounted amplifiers, subwoofer enclosure, and speakers), keeping only the stereo head when I installed the 6.5" Roadster Sound subwoofer enclosure. I now use a JL Audio 300/4 amplifier to provide 75 watts RMS to each of the four speakers. I removed all stock speakers. The new front speakers are Focal 130A stock-size component items, and the rears are 4" Polk DB400 Coaxials. Yes, I have blown a few other sets of speakers during the past year, but I like my sound LOUD! An MTX Audio Road Thunder RT202 is dedicated to powering the subwoofer, with two channels that bridge to provide 150 watts RMS at 4 ohms. (photo 1, MTX on the left, JL Audio 300/4 on the right) I also employ a BassCube dimensionalizer, as recommended by Roadster Sound for the sensation of even more output. The device is not required, but when it comes to bass, I believe that "if more is better, too much is just right!" (photo 2, trunk mounted BassCube) I will keep the same amplifier setup, and now only have to swap out the Roadster Sound 6.5" speaker enclosure for the larger one, and add an 8" JL Audio 8w3v2 speaker.

I have been waiting with great expectations for the 8" version the Roadster Sound subwoofer enclosure since I learned a while back that it would be offered as an alternative to the 6.5" model. I have enjoyed the added bass provided by the 6.5" Roadster Sound enclosure with the JL 6w0 subwoofer since installing it a year ago. The improvement in bass volume and quality over the stock Harmon Kardon system was impressive. Still, I wanted even more bass, and the larger 8" setup was the logical next step.

The new 8" enclosure is a more high-tech item than the 6.5" model, and shows a greater degree of sophistication in its construction. While the 6.5" model is made of high density particle board, the 8" model is mostly heavy molded plastic-like material. The top portion of the 8" model is thick and wood-like; possibly fiberboard, and is covered to match the interior of the Z3.

I will describe the installation process I followed from the point of already having the 6.5" unit installed. There are some additional steps required to ensure proper fitting of the new, larger 8" box, and you should also refer to the detailed installation instructions that Roadster Sound provides. It's not that difficult, but it will take several hours to do the job right, so budget several hours - plus some extra time on another day, as you will have to wait for sealant to dry; and have a few tools handy. I found that the following items made the job move right along:

1. A quality drill and ¼" sized bit for drilling 6 holes (three into the car and three into the plastic enclosure). The bit must be sharp for drilling into steel.
2. Philips screwdriver (large) for starting the sheet metal screws
3. An offset Philips screwdriver to install the two screws inside the box once the top is attached; this is essential.
4. Better than #3, above, is a ratcheting offset Phillips screwdriver. The one I found cost less than ten bucks at my local hardware store, and since I ended up installing, then removing the box several times to get it just right, it was seriously worth it!
5. A razor type boxcutter knife to cut off a plastic "ridge" inside the cavity to accommodate the box.
6. A hacksaw blade (the entire saw is not needed, just hold the blade - but use gloves!) for cutting off more plastic (see the photo).
7. If you like to use a lot of silicone sealer (like I do), pick up an extra tube of RTV Blue. Roadster Sound includes enough, but I wanted to ensure that there was no possibility of air leaking out of the box, and sealed it all up good.
8. Extra Dynamat to deaden vibration and add extra mass to the enclosure.
9. A heat gun to make the stiff Dynamat more pliable during installation.
10. A soldering gun and soldier to ensure the electrical connections won't be shaken loose.

The installation

The Roadster Sound enclosure arrived by USPS, and was professionally packed to afford its contents protection during shipping. (photo 3 and 4)

The contents included (photo 5 and 6):

1. The unassembled enclosure (the lower plastic shell, and top piece)
2. Two sizes of wood screws of the type that would be used to attach the speaker to the enclosure top piece.
3. The electrical block for adjoining speaker wire connections
4. A length of wire and terminals for connecting the speaker to the electrical block
5. Two small tubes of RTV Blue silicone sealer
6. A section of Dynamat sound damping material

Getting started

I have to admit that I was not prepared for the degree of hands-on assembly. I had not actually read the online instructions, and upon opening the box, realized that I had my work cut out for me. First step: back to the Roadster Sound web site for instructions.

The next step is to remove the old (in my case, Roadster Sound 6.5") enclosure. My unit as such a tight fit that I had to drive two screws into the box and yank it by the screw heads with pliers. There is simply no other way to grasp the enclosure (photo 7).

The resulting cavity shows evidence of my earlier trimming to accept the 6.5" Roadster Sound enclosures. Additional enlargement will be necessary for the 8" unit. Once you attempt to drop the enclosure into place, it will become obvious what parts need to be removed (photo 8). Begin by removing the ridge of plastic from the rear interior of the enclosure. Use the boxcutter knife for this (photo 9). The next thing to go is the metal bracket towards the front of the car. Remove the screws and lift it out (photo 10). This is what remains (photo 11). Next, use a hacksaw blade to remove the plastic tabs that the metal bracket was attached to (photo 12).

Follow Roadster Sound's instructions for drilling holes into both the car and the enclosure, and positioning the rubber washers (photo 13). An assortment of washer of varied thickness are provided to allow you to set the height of the enclosure to be flush with the existing top piece (photo 14). This step will require you to temporarily attach the top piece to the enclosure (no glue yet).

Once I had established which rubber washers to use, I found that contact cement kept the washer stacks neatly together while I continued the assembly (photo 15 and 16).

Assemble the wiring block into the enclosure and seal the whole thing with RTV Blue to prevent air leaks (photo 17).

Before attaching the top piece, I added extra Dynamat to the inside of the enclosure for added mass and to reduce any vibration. I did not add much, so as not to reduce the interior volume of the enclosure (photo 18).

Once the holes are drilled for the enclosure and the car, the top piece can be glued onto the enclosure. Again, use RTV Blue for this (photo 19). This will take a few hours to dry.

I added extra Dynamat to cover nearly all the exterior surface of the enclosure (not the bottom, which would interfere with how the enclosure would screw into the car.) Dynamat is very stiff, and becomes pliable once warmed with a heat gun (photo 20 and 21). The complete Dynamat-wrapped enclosure is now ready to install into the car (photo 22).

Now is a good time to start the screws into the holes. You will need an offset screwdriver for this task. A ratcheting screwdriver will make the job much easier (photo 23).

Attach the speaker wires to the binding posts (photo 24), and drop the enclosure into place. It should fit neatly flush across the top (photos 25 and 26).

Install and tighten the three sheet metal screws into place (photo 27). I actually had to do this step several times, and came to appreciate the ratcheting screwdriver.

To ensure an air-tight seal between the speaker and the enclosure, I put a layer of thick rubber tape around the mating surface of the enclosure top (photos 28 and 29).

Now for some electrical theory: Ohm's Law. Amplifiers seem to be rated at either two ohms or four ohms. It DOES matter that you match the ohms from your amplifier to your speaker. The JL Audio 8w3v2 speaker is available in a 2 ohm or a 4 ohm version. But, you must remember that this is a dual voice coil speaker, meaning that there are actually two coils, each being either 2 ohms or 4 ohms. Since you want to use both coils, you will either have to wire them in series or in parallel before connecting the speaker wires. Wiring the voice coils in parallel will result in halving the resistance in ohms. Thusly, a dual-coil, 4 ohm speaker wired in parallel will have a total resistance of 2 ohms. On the other hand, wiring the voice coils in series will result in the ohm values being added. If you used a 2 ohm speaker, you will then have a total of 4 ohms (2 ohms per voice coil), which will match a 4 ohm amplifier. This is the configuration that I used.

Attach the speaker wires using the crimp-on connectors, and drop it into place (photos 30 and 31). Now screw in the 8 woodscrews (photo 32). The final result is a very professional looking installation (photos 33 and 34).

A look in the trunk shows a nicely fitted set of amplifiers and a BassCube - all highlighted by blue LEDs which are wired into (and instead of) the trunk's white "dome" light. (photo 35) Space being at a premium in the trunk of a Z3, I mounted the amplifiers to an 1/8 th " sheet of diamond plate aluminum, bolted to the steel underside of the trunk roof. All wires are routed through the trunk liner for a neater appearance.