UrS4: Bosectomy (Part 2)

In Part 1 of this series, I outlined the plan for my stereo upgrade, removed the door panels from the car, and removed the Bose speaker module, which was secured to the door with six Philip screws. I discarded the module, because I will be upgrading the woofer from 4″ to 5.25″ and I could not see how the module could be used to help secure the new woofer to the door. For some applications, it might be possible to reuse the Bose door module with a replacement driver. If chosen carefully, component speakers and a crossover could also be secured inside the door module. I had hopes for a truly stealth installation, but it was no use. The MB Quart crossover I am using is as big as a breadbox. I swear it looks like one of those Radio Shack science kits from the 70’s. More on this later.

On that note, the stereo components which I have chosen will dictate some of the design and installation parameters, in which I have to work. I will point these out whenever possible, but of course, your mileage may vary, according to the components which you select. If you read these articles before you buy, they might help you make a more informed choice. So, here is what he have so far:

Top Tip: For easier installation, select separate door speaker components that utilize a 4″ driver and a small crossover unit, so that the Bose door module can be reused.

However, for better sound quality, you will want to select a 5.25″ woofer. It will fit (with some work) and it will return a much better sound.

Tweeter Installation

Let’s start with something easy – tweeter installation. Take an X-Acto knife and cut away the soft plastic behind the built-in tweeter grille. Then fit the tweeter behind the grille and secure in place with a bracket. In non-Bose stereos of the era, there was an actual tweeter (Nokia!) mounted behind the grille, so there are factory mounting points.

Woofer Installation

Nothing too difficult here and not much that is UrS specific; these are just basic concepts. I started by making a cardboard template for the mounting board. This took awhile, because door panel isn’t perfectly square and I couldn’t figure-out how I was going to secure the mounting board. The secret was to square it up by using a spacer.

Once the spacer was in place, the mounting board would sit square and be closer to factory mounting locations that I could use to secure it.

I cut the mounting board with a jigsaw and mounted the woofer to the front with a supplied mounting frame and four screws. Try to use screws that barely extend past the mounting board. I had to cut-down one of the screws, because it interfered enough to keep the door panel from going back on the door.

I cut a piece of acoustic foam to fill the unused void around the woofer and behind the area where the tuned port used to be and then set the mounting board in place, on top of the foam. To secure the board in place, I used three different methods, two of which you can see in the photo above. On the left, that piece is directly above the spacer and the top fits within a groove that is already in the door for a very secure fit.

This simple metal bracket holds the bottom of the mounting board.

This is what it looks like from the front. I used an X-Acto knife to trim the opening so there isn’t any material blocking the speaker. I didn’t discover until later that the light-colored foam could be seen through the grille, so I put a piece of black foam over most of it and then went after the rest with a Sharpie.

Crossover Installation

The crossover was challenging. I had a couple of design hurdles and considerations. First, the crossovers are huge. I have no idea why, in this day and age, a crossover can’t be the size of a matchbox, especially in an automotive application. The second consideration is that the crossovers are adjustable. So, I needed to figure-out how I could make adjustments while listening to music, without having to remove both door panels. One option is to simply mount the crossovers inside the cabin of the car. The glove box might work, or maybe the trunk (where the amps will be going), but both of these options have other problems, including the amount of wiring that needs to be done.

My solution came to me after Cat-Cat found a good mounting location. I found a place with some factory mounting points nearby and where the crossover would not interfere with the window regulator.

Top Tip: Use the Bose door module as a template to see where there are cutouts for the window regulator. Avoid those locations for your components. This will help reduce the number of test fits you will need to make.

I noticed that the mounting location was mostly located behind the door panel’s storage bin. At that point, I thought it would be acceptable to me to cut an access hole for the crossover adjustment knob, through the door panel, but mostly hidden by the storage bin. Since, I would be cutting a hole in the door panel and through the factory vinyl insert, I knew that this design decision would also mean some project creep. If I were going to cut holes in the vinyl fabric, I might as well concurrently replace the vinyl with Alcantera. See? This is one of the reasons it takes me years to get anything done.

The first step was to mount the crossover and then test fit the door back into the car. Good thing I tested it, because I had to move the crossover down to clear the inner door frame. I had to cut off one of the factory mounting points to get it to fit. That was just as well, since the new location put the visible control even lower into the door bin. Once the crossover was mounted, I measured twice, removed the crossover, and cut the hole for the adjustment control. I could have made the hole smaller, so that it perfectly matched the diameter of the control, but then I would have had to find or fabricate a finishing bezel. Instead, I decided to use one of the unused tweeter mounting rings. This made the hole bigger, but I thought it would give the install a more professional look.

This is the proof of concept. I figured if I didn’t like it, I could just seal the hole back up and the door fabric would cover up my experiment. I decided to move forward, which meant first replacing the factory vinyl door liner with Alcantera.

Bonus Door Liner Replacement FAQ!

This will be brief, because I don’t actually know what I am doing. I pulled off the original vinyl material (which was already coming off anyway), and discovered that Audi had chosen to affix the material to the door using…bee pollen. Why? I don’t know. Maybe because they knew that honey bees would soon be as extinct as unicorns and that their pollen would be as rare as the unicorn tears and dinosaur egg shells used in other parts of these cars. Thanks, Audi. Anyway, this bee pollen is nasty stuff. It’s sticky and it just disintegrates when you touch it. Even with judicious use of Goo-Gone (you guys know how much I love Goo-Gone) and a gasket scraper, I never could get rid of all of this stuff.

I keep saying Alcantera, but that’s a brand name. I really just went and bought some fake black suede from Hancock Fabrics. Then I found a roll of foam sheet from Michael’s hobby shop. I used the original vinyl as a template and cut the foam and pseudo-suede. Then I glued those two pieces together. I used a Krylon adhesive, based on a recommendation I got at Michael’s, but I already see where I have to go back and re-adhere some material, so I will be using some 3M 90 Heavy Duty Spray Adhesive.

Once I had the fabric sandwich together, I glued down the big, flat area first and then worked out to the edges, which I tucked into grooves at the edge of the panel. The foam was so thick that I kept having to trim it down so that the cloth and foam combo would fit into the groove. This was very aggravating, because if you trim too much, then the material won’t fold into the groove at all anymore and you either have to live with it, or start over. It might be easier if you don’t use the foam, but I didn’t think the fake suede material was thick enough to use on the door by itself. By gluing it to the foam, you also eliminate any wrinkling of the fabric.

Then I used magazines to press the fabric to the door, while the adhesive dried. It turned-out okay, but it is very difficult to reach the part at the bottom of the door, because of the storage bin. Luckily, you can’t see down in there very well.

This is the door, when it is almost finished. You can see the crossover control peeking-out from behind the storage cubby. You can also see that I hadn’t yet hit the acoustic foam with a Sharpie.

Here is a close-up of the crossover control after I have pressed-in the tweeter surround bezel. You can see some Dremmel marks, so I will probably hit it with some Plasti-Kote. The control dial looks off-center, but it’s not.

Finishing Up

All that’s left is to wire it together and reinstall the door. Nothing much to say here. You should probably know how to wire a stereo, if you are undertaking this project yourself. Besides, the instructions that come with your components will explain what you need to do. Because of the way I am going to wire the system, I will not be using any (or much) of the factory wiring. I have left it in place for now, but I made tidy little custom harnesses for the speakers and crossover.

Using heat-shrink tubing or other wiring wrap will help the wire fit securely into the factory clips, which you can see in the photo above. The clips are nice and can moved to various helpful locations on the back of the door.

This is the back of the door, which shows everything. Note the location of the crossover, which will not interfere with the door.

And this is the finished door.

I am very pleased with the results. The fabric refinishing isn’t perfect, but I can go back and either fix it or try again. It will be easier the second time around (or fifth time around, since I now have to do my other three doors). I like the crossover control, too. If I wanted to hide it further, I can click the unused tweeter grille into the bezel, though people might wonder why I have a tweeter inside a storage cubby.

In Part 3, I will discuss installing the rear speakers, amps, and more wiring.

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