w126 custom back deck how-to! - PeachParts Mercedes-Benz Forum

tbomachines · #1 06-21-2009, 01:39 AM

Hello! 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 (1982 300SD) I was surprised to see that it had a digital FM radio and four speakers with fader. Good for the time, but things have changed. So, 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. So here's how it went, and how you can do the same if you wish.

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.

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.

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.

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).

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 hope that this can help and contribute to the great wealth of knowledge in this forum! Thanks! --TC

Next post will have pictures 6-8.

tbomachines · #2 06-21-2009, 01:41 AM

Rest of the pictures here. --TC

toomany MBZ · #3 06-21-2009, 09:37 AM

Nice job, now do mine!

tbomachines · #4 06-21-2009, 11:14 AM

Hehe if you're willing to pay the 6 hours of labor I'd be happy to! Really it wasn't that hard though, just time consuming and a bit tedious with the trimming. I totally winged/eyeballed it (no real measurements or anything)
and it came out great, I'm confident anyone with the time and tools can do an equal or better job. Plus I'm not so hot with upholstering, only the 3rd thing I've ever had to upholster.

I guess today would be a good day to thank my father for teaching me some good woodworking.

toomany MBZ · #5 06-21-2009, 01:17 PM

Quote:

Originally Posted by tbomachines

I guess today would be a good day to thank my father for teaching me some good woodworking.

I think you're right.

My head unit needs replacing, modern HU's are quite a bit different as to the wiring.

tbomachines · #6 06-22-2009, 08:30 AM

Quote:

Originally Posted by toomany MBZ

I think you're right.

My head unit needs replacing, modern HU's are quite a bit different as to the wiring.

Also, you should check on the resistance of the speakers (I'm sure its on here somewhere). IIRC the stock speakers are 6 ohm with the fader, which is an odd number. Most systems should be okay with it but it can't hurt to double check it before you overheat a new HU--so if you're thinking about replacing the speakers and bypassing the fader its a good idea to do it all at once.

Some diligent internet searching might turn up a plug-n-play adapter to help with the wiring so you don't have to splice into every one.

Dee8go · #7 06-22-2009, 12:13 PM

Will you be putting a sub in there too at some point? I was just wondering how you'd go about sizing a sub for the trunk of a 126. There's a gas tank in between the trunk and the inside of the car. How would you determine what it'll take power-wise to get through all of that?

tbomachines · #8 06-22-2009, 06:05 PM

Quote:

Originally Posted by Dee8go

Will you be putting a sub in there too at some point? I was just wondering how you'd go about sizing a sub for the trunk of a 126. There's a gas tank in between the trunk and the inside of the car. How would you determine what it'll take power-wise to get through all of that?

I actually built the box last night. It is 15 inches tall x 20 wide x 14 deep. It houses a 1500W 12" Kenwood sub, also with a 4" port tube extending 7" into the box (what a mouthful!) and I will route it up to the deck. This puts it somewhere around 1.5 cubic feet which is ideal for the single ported 12". I'm not looking for extreme wake-up-the-neighborhood bass, just something to fill out the bottom end a bit since the 6x9s are good for midrange. I'm hoping the port coming out the deck will help a lot with hearing it in the passenger area, even if not the thing should be more than loud enough. Today I ordered a BOSS 1200W monoblock amp (I'm going cheap, we'll see how it does) and some Pioneer 4" to put in the front speakers to really pop the high and mids up front. I don't anticipate cranking up the amp too much.

As for trunk space, well it isn't very good now. The box doesn't extend past the top lip, but it is right on the edge. It takes up about 2/3 the way across. One Idea you could do is cutting out the space from the top of the trunk frame (NOT above the tank!!) and putting the sub there with a board behind it in the trunk for a large shallow box. I chose not to cut since I don't know how structurally important that area is, plus it would scar the car forever if you mess it up.

Dee8go · #9 06-22-2009, 11:01 PM

How cheap is "cheap?" I'd like to put a sub in the SEC, but I'm really strapped right now. I had thought of using the infinity Basslink since it has the enclosure and amp all in one. I have no idea how that would sound, though.

tbomachines · #10 06-22-2009, 11:26 PM

Sub was $50 from an Amazon special a few months ago, I think its about 75 normally which still isn't bad since its a fantastic sub. Its a Kenwood KFC-W3011, and I just realized it was 1200 instead of 1500W...still plenty for me. Amp (Boss Audio D1200M Diablo Class D) was $80+shipping, one of the cheapest I could find since I don't care about super high volume. Add in building cost plus time and thats it. I think thats still better than the infinity price-wise if you're willing to do the work. I've heard good things about the Basslink and Infinity is a good brand in general (Kappa series is awesome!). Probably not going to be big and booming though, just a full bottom-end if that is what you're looking for.

One question though, do you still have the stock speakers in your car? And head unit?

I hear ya about the money, I probably should have just gotten new injector nozzles in hindsight....

Dee8go · #11 06-23-2009, 08:00 AM

I took out the stock paper speakers and replaced them with Infinity Reference speakers. They're great! I replaced the old aftermarket CD player with an Alpine MP3 players which is also awesome. I'm not looking for a lot of boom, just a fuller bottom end. I'd like to get that for what you paid for yours. That's great.

donbryce · #12 06-23-2009, 08:26 AM

Quote:

Originally Posted by Dee8go

How cheap is "cheap?" I'd like to put a sub in the SEC, but I'm really strapped right now. I had thought of using the infinity Basslink since it has the enclosure and amp all in one. I have no idea how that would sound, though.

I've been running an Infinity Basslink in the trunk of my 380SE for years now. Absolutely super sound for the size, and money invested. I made a bracket to allow mounting on the left side of the trunk in the recess off the inside of the fender. I first tried a Kenwood WOOX, but it wasn't nearly enough power, so now the bracket is used to hang the Basslink. I found the post from years back with a picture of it, below.
Much has been posted about the gas tank and the poor acoustics of the 126 trunk for bass in the passenger cabin. IMO, this is rubbish. The storage shelf pocket and first aid kit pocket are made of thin plastic, acoustically transparant for bass waves. The sound moves up and over the gas tank and right into the interior.
I have another Basslink in transit right now for the 560SL, new off EBay for around $250.00, vs. the outrageous Future Shop price here of $399.99. The original in the 380SE was used, also EBay, and IIRC cost about $175.00 delivered. There's a newer version with 250W RMS (older one is 200W), more money and it's bigger, so I decided to stay with the original.

Dee8go · #13 06-23-2009, 10:32 AM

Thanks, Don. That's just the kind of info I was looking for. The SE would be quite similar to my SEC as far as this goes, I would think. Now, all I need is to scrape together some coin and get one on order.

tbomachines · #14 06-23-2009, 10:51 AM

I'm inclined to think that the black trays would probably rattle around quite a bit with heavy bass. If keeping the back deck, I'd take out the black trays and replace with fine black mesh so there is little air resistance and greater projection.

Also if you haven't already you should jump the fader in the center console, it is a needless source of added resistance and possible source of noise/poor connectivity. If you feel really gung-ho, the old wires are also usually junk by now too, any 20+ year old car could use a good re-wire. w126 is pretty easy to do it on.

Don, how much wiring is involved with the basslink? I'd imagine you still need to run all the usual amp lines like 4/8g fused wire from battery, acc, ground, RCAs to HU.

Considering, it might not be much easier getting a single unit seeing as there are pre-made boxes readily available fairly cheap. IMHO the time it takes to mount a separate amp is worth saving a hundred or two bucks. Not trying to persuade you out of getting the Basslink, it has excellent reviews--but if money is your priority you can definitely do it for half the price and get a more fitting system.

Dee8go · #15 06-23-2009, 10:55 AM

It's a moot point at the moment, as I have not the funds to go either way. I'll just have to see what opportuities present themselves, I guess. I was going more for simplicity than anything else. Plus, I'm fond of Infinity's products.