W126 (300SD) custom 6x9" speaker and back deck install

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I wrote up this how-to for one of the forums, recently dug it up and realized how awesome this build was. Let me first start out by saying I'm an audiophile and there is nothing that annoys me more than poorly placed/EQd speakers and poor quality music. When I got my w126 (Boxy, 1982 300SD) I was surprised to see that it had a digital FM radio and four speakers with fader. Good for the time 30 years ago, but things have changed. The old paper elements were almost certainly blown or rotted, and tiny in size so sound quality would certainly be an issue.  Looking at the compartments on the rear deck (called a "hat rack" in the FSM) I realized I could squeeze a couple of 6x9s in there with some elbow grease.

Things you'll need:
- Big board of wood, MDF is cheap and easy to work with, which is what I used.
- spray adhesive (3M super trim adhesive, $10)
- wood glue
- hand-held jig saw
- drill (for jig saw start points)
- Fabric. I used Vinyl from Jo-Ann, pretty thick and tough stuff. I used 30 inches of it. (Picture 9) I got the color almost exact to the existing trim.
- 2 speakers. The ones in the picture are dummy speakers, old ones I don't care if ruined.
- speaker template will make your life a lot easier. I didn't have one so I tried using a grille from another 6x9, which worked okay.
- staple gun

First, remove the rear sear and take off the "hat rack" per FSM instructions (basically take off side pillar covers then lift the thing out). This was kind of a pain since it was in there quite snugly. Once that is out, get yourself a big ol' board of wood.

Take your back deck and place it on the board of wood. This will serve as your template. Trace around the edges with sharpie to get a rough outline of the piece. Cut it out (picture 1). It will take a number of tries and quite a bit of trimming to get it perfect, but once you do, it will look great! One note: I chose to place it OVER the trunk hinge, you can also cut a notch from the board but I thought itd look ugly.

1

Okay, so the next step is to figure out where you can place the speakers. I put them as far to each side as I could while still in the cubby holes. I placed a piece of paper over the holes, marked where the speakers were, then transferred it to my template. Fine-tune the placement (including symmetry and angle) of the speakers with the supplied template or grille and cut (measure twice cut once!!).

I decided to put spacers in to raise my speakers a bit. This was probably unnecessary but I didn't want them resting on the fuel tank. I simply traced around the speaker grille, measured an inch, then went around in the circle to connect the dots. (Picture 3) Drill holes, insert the saw, and cut away! Picture 4 is what I ended up with x2. Picture 5 shows them on the speaker.

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5

After this, glue the spacers to the speaker holes, make sure everything is snug and where you want it (pictures 6&7). Let it dry a bit. At some point I thought it was a good idea to cut a hole in the deck for use with my subwoofer, which I have yet to install.

6

7

You're ready for the fabric! This is just like doing any car upholstry. I'll admit I am not very good at it, and it kinda shows. However, this isn't too bad, and the curves are all covered up by speakers! Anyway, stretch the fabric over the front. You could angle it at the spacers for a more "boxy" effect, but I chose not to. Use the spray adhesive to coat the entire front section, then apply the fabric. Use stuff to hold it down while it sets, and make sure there are no air bubbles. It dries very quickly so you have to work fast--hence why there are no pictures of this process.

Once it dries enough, turn it over and stretch it over the back. Staple it as much as you can so that there are no visible creases in the other side. Apply more adhesive if necessary.

Thats it!! Let the adhesive dry a bit more, throw it in the car, and install speakers! Picture 8 is the finished product with a few air pockets that need to be pressed out. In all it took me about 6 hours to do with trial and error, but the result is fantastic. When I get my subwoofer in place I will take care of the box air port I already cut (and re-glue the vinyl).

8

As for sound, even the dummy speakers are a vast improvement over stock. My only complaint about the sound quality is that there is not enough stereo separation, but only a minor complaint. As far as frequency setup, it is pretty good since the rear window deflects a lot of high frequencies directly toward the occupants.

I will be reupholstering this deck in blue to match the white car's interior.