The BMW 550i has the Logic 7 sound system which sounds OK, for the most part, but it’s a little weak, mainly in the mid-low region. I have owned many vehicles and I must say that they all had “less than appreciable” OE sound systems but the Logic 7 is by far the best “out the gate” system in a car I have ever owned. That said, it still lacks. As you all may know, BMW places a shallow 6” sub underneath the front seats in most of their vehicles. After speaking with a friend, I decided that the only thing the system really needed was a little more bass and decided to keep the factory 6” subs and let them play mid bass. Wanting to keep a stealth feel to the system, I chose the JL Audio 6W3v3-4. It was also convenient because I had two laying around the shop that were from a previous build that the customer never came back to have installed after he ordered them. All I needed now was an amplifier. Just so happens I had an Audio Systems Twister F300 laying around too from a similar situation (glad they were paid for in advance)!
Since the 550i is my daily driver, I did not want to sacrifice trunk space so the equipment I had was perfect. Not wanting to cut on the car but keep the bass in the cabin, firing the subs through the ski hole would be perfect, only if it had one! Wait, I can make one! Once the rear seat is removed you will find that it is just 1/4” ABS in the “ski hole” location.
Removing the trim panel, I cut a perfect square and transfered it to 3/4” MDF, making 2 inserts (needed 1.5” depth to clear rear of seat).
Next, I transfered the inside of the opening to the trim panel and flushed it in, creating a seamless ski hole. I made several more of these shapes for the front of the sub enclosure to serve as a mounting plate and ensure no air escaped. A piece of grill mesh wire was attached with two-part epoxy and the trim panel was then covered in black suede for an “OEM” appearance.
Three-quarter-inch MDF was used for the sub enclosure as well. Once the enclosure was built I had to add a “cap” to it and seal it with silicone (some use caulking) to again ensure that no air escaped between the rear seat and the cabin. Since the rear seat sits at about a 30 degree angle, I had to build a stand for the enclosure to sit flush against the rear seat.
With all enclosures, you want to ensure that they are securely mounted. In this case I cut metal brackets, bent at 90 degrees and mounted to the enclosure and used the rear seat attachment points. The amplifier was mounted to the top of the enclosure and the wires ran neatly across the rear shelf. Because the enclosure now sits at an angle, a plate was made that sits on a negative angle so the trim panel will sit vertical at 0 degrees.
Now the fun part, trimming the trunk. Although this is my daily driver, I am in the process of doing a complete Hartge (European BMW Tuner www.hartge.de) conversion and thought it would be a great idea to incorporate that logo into the install. I also wanted to give JL Audio some props because those lil 6W3v3ʼs ROCK! With that being said, it must still be clean, simple, and not take away from the overall appearance of the vehicle…here goes. Make a template of the space using chip board first. Then transfer that to MDF, in this case 1/4”.
Remember, the trunk must remain functional, so do not cover those luggage tie downs! Tape off the area and fill in any gaps with duraglass/kitty hair, etc., creating a tight pressure fit. The vertical piece and the flat piece are now my platforms and I can begin to configure the trim panels. Again, do not forget to integrate the OE pull & attachment points.
Remember that Hartge logo, I created it using vinyl letters for a mock up and drew the shape around them. I then used my table mounted router the trim the shapes out. I also added 1/4” acrylic for a cool lighting effect.
To give JL Audio their props for making a great small sub I decided it was time that this Install was almost over and made the JL Audio Watch! Once you have your idea, draw it out on the material of choice and then get some straight edges and curves and route the shape out that you want.
To keep the light theme going, I added a piece of 1/4” acrylic to the watch bezel as well. Once I was satisfied with the overall fit, I wrapped the entire trunk in the same black suede that I used on the rear seat trim panel. The platform pieces of the trunk received matching exterior color black sapphire metallic paint. For the bottom platform, the Hartge logo was painted in the Hartge blues & silver metallic for the letters. The JL Audio watch band was wrapped in a grey suede for contrast, as well as the trim for the Hartge logo. The subwoofer level control was place near the gear selector for easy access. Whatʼs left is a nicely integrated OEM sound system that retains the trunk and sounds great! Phase 1 of the Immortalization process complete. —Yusuf Boyd
