1. Carefully remove the subwoofer enclosure cover by first lifting rear edge of cover and then lifting entire cover straight up. Cover should lift out with minimal effort, but may require some additional effort to release the rear snaps. Take your time and be careful when removing the sub lid! The easiest thing to do is to use a flat, metal, handled-tool like a 5-in-1 and carefully pry each side up like this.
   
2. Remove 4 mounting screws (2) from existing speaker enclosure (1).
   
3. Remove enclosure (1) by pulling upwards. Disconnect wiring harness connector (2) and remove entire enclosure from vehicle. Using a socket wrench, loosen and remove the brackets that the original factory enclosure was attached to.
   
4. Remove 4 existing clip nuts (1). With a knife, diagonal flush cutters or small saw, carefully trim away two center plastic extrusions (2).
   
5. Trim the plastic ridge from the back of the compartment like as shown using a small hacksaw (you can pick one up at a hardware or home improvement store for less than $5), a Dremel, or other tool of choice. Click on the picture at right for a more detailed image.
   
6. Carefully remove foam padding from rear of speaker compartment.
   
7. Remove backing from Aluminum-skinned Sound Matting and apply as shown (1). Press matting firmly against panel to ensure complete adhesion. CAUTION: Take care when working with Sound Matting due to sharp edges.

   

8. Apply a small amount of contact cement or super glue (2) to one side of each 3/4" (larger size) rubber spacer (1).
   
9. Carefully pull back rear panel and place spacer (1) between metalwork and plastic panel as shown in left rear side of speaker compartment. Place glue side against the plastic panel. NOTE: These spacers hold the plastic panel away from the woofer cone and provide clearance. In addition, they help to minimize or eliminate the rear panel bowing out in the middle due to contact with the speaker gasket surround.
   
10. Repeat step 8 for the right side.
    
11. Attach the 4 wire terminals to the speaker wire. Attach the wire to the plastic terminal cup, and note which wire/terminal is negative. Using the four 1/2 " screws provided, install the terminal cup in the recess/hole in the side of the enclosure. Tighten the screws CAREFULLY, taking care not to strip the screws or split the plastic terminal cup. Then attach the speaker wire to the speaker.

12. Attach the speaker to the enclosure using the 4 included screws, making sure the speaker wire is not trapped between the rear of the speaker and the enclosure rear wall. The back of the speaker mounting lip should sit flush against the recessed lip and form an air-tight seal, if it does not the speaker wire is in the way. It is a tight fit. Be careful not to overtighten the screws - they will strip. Just tighten them to about 1/2 turn past snug. If you do happen to strip a screw, remove the speaker, put some superglue in the stripped hole, let it dry, and then re-attach the speaker.

13. Using the 1" screws, screw the 1/2" rubber spacers to the front of the enclosure, about 2/3 of the way to the top of the enclosure, next to the speaker. To get the screw started, place the rubber spacer on a firm surface and screw the screw right through the center of the rubber, then screw into the enclosure. This helps stabilize the enclosure in the compartment and keeps it away from the back of the compartment. NOTE: The rear plastic panel will initially bow out beyond the top cover. This is due to the initial tight fit. The panel will return to flush over time, as the rubber spacers, foam padding, etc. compress and settle in. This should take about a month (less in hot weather).

14. Cut and affix the foam padding to the bottom of the enclosure as shown. (Click on the picture for a larger image).
    
15. Connect the wires from the amp. I chose to cut off the BMW plastic coupling, you may wish to leave it. I soldered both pair of wire together to make one pair, but it isn't really necessary. Just make sure it is connected to the amplifier correctly.

16. Carefully drop the enclosure into the compartment. You will need to push on the back plastic part of the enclosure to clear the 1/2" rubber spacers. NOTE: If your enclosure does not appear to have enough room between the back plastic panel and the enclosure itself, loosen (do not remove them) the three screws at the bottom on the outside of the back plastic panel. Then push and hold the panel out as far as possible and retighten the screws.

17. Expose the adhesive stip on the back of the black foam rubber padding strip and attach to the rear of the enclosure at the top edge of the angled ends. This foam will prevent the enclosure from rattling against the curved plastic panels on the forward part of the sub compartment. (Attach the foam to the enclosure at the location where this picture shows clear plastic tubing).
    
18. Test everything out.

19. Reattach the top of the compartment - you will need to attach the back first. The second side will require some pressure, it is a snug fit.

20. Be sure to use the cloth window protector that came with your Z3 when the top is down (a towel will work as well). This will prevent the vinyl window rattling. It will also keep the window from getting a small line of hazing scratches. In most Z3's the back window does not touch the back of the sub compartment with the top down, so this step won't be necessary if you are one of those people. The cause apparently stems from the fact that BMW's tolerance for internal panel installation is +-1/8" - I must be on the high-end of that.

21. IMPORTANT: The JL 6w0 requires some break-in time. The preferred way to do this is to hook the car up to a battery charger and play a 25Hz or 30Hz test tone at about half-volume for 8 hours. An alternative is to play a wide variety of bass intensive music for at least 8 hours before you really crank the system. The break-in process gives the spider and foam surround some time to soften up.

22. A bass enhancement device like the Phoenix Gold BassCUBE (~$155) or the Kicker 03KX3 (~$110) will significantly improve bass in the 35-50Hz range. I added the Phoenix Gold BassCUBE to my system with outstanding results. Any bass enhancement device will work well as long as it has a "narrow" or "high" Q setting and that it provides it's bass boost at between 37-40Hz (VERY IMPORTANT). If you'd like to get a bass enhancement device and have questions email me and I'll help you select and install one. If you purchase the BassCUBE, here is a copy of the dealer installation manual, which will cover how to configure and tune it. This manual isn't included in the retail box for the BassCUBE.

Pictures and feedback are welcome and appreciated!