This car came with a set of non-folding leather (?) rear seats in it. This is nice to have, and a pricey aftermarket option, and will perhaps come into play when my son gets a little older. But these seats are so small as to be generally useless; the car came (in the US) with a carpet-covered wooden deck in that place. Unfortunately, this deck was lost along the way.
As the stereo system was nothing to write home about, due to the tiny 4" dash speakers, a natural idea was to install speakers in a rear deck. So I set out to build a new rear deck. The idea was to be able to switch easily between the speaker system and the rear seats.
I did a lot of measuring, and sketched out a shape on a piece of 1/2" plywood. I cut this out and fit it into place, there was some trial-and-error trimming required. Next, I cut some vertical front pieces to fill in most of the holes. I left some opening for ventilation. After this, I picked up a set of 6x9 Infinity speakers and cut out holes for these. As the Alpine 7805 head in the car had line-level rear speaker lines only, I mounted a (used, from a pawnshop) 25W/ch Alpine amplifier under the deck as well. The speakers and the amplifier nestle in the pockets that are there for the seat cushions, the deck is flush with the top of the 'hump', as is normal. The seat belts are still in the pockets, wrapped in old socks so they don't rattle around.
While I was at it, I installed a set of 3.5" Infinity speakers in the dash to replace the stock speakers. I used some series capacitors to block bass (über-cheap crossover), so that they wouldn't bottom out. Bass was to be the job of the rear speakers anyway.
The real fun was in routing the wiring back from the head unit. I had to run two coaxial line-level cables from the head back. I also had to run power from the fuse box and the accessory power-up line from the head unit. All of this new wire ran down the wiring channel under the passenger-side door sill. It barely fit, as that channel is already occupied by the heavy battery cable.
With all this equipment fitted in place and comfortable, and with everything connected, I fired up the system and it seemed to work well. So I removed everything from the deck and took the board to a local upholstery shop. They were able to find a back-less carpet type in a compatible color, Biscuit, at not too bad a price. They fitted the carpet to the board, which I brought home and re-installed.
It looked great, and sounded a lot better than it did before.
But, after using it awhile it just seemed to lack bass. (I'm not a car-rattler, I just like a good frequency range.) It seemed apparent that I should have gone for 10" rounds, or something else bigger than the 6x9's. There was room, barely. However, the holes had already been cut, and the carpeting paid for. It was beyond the easy experimentation stage.
As an experiment, I bought a 12" speaker that was in a small cube enclosure (also a pawnshop item). It sounded OK on the home stereo, so I procured another car amplifier (pawnshop!), a 35W/ch bridgeable one. I managed to get it stacked under the original deck amplifier, and wired it in parallel with the signal feed. I flipped its switches to invert one channel's input, and connected up the cube speaker to the bridge outputs. I also flipped the low-pass switch, to only let low signals into it. (This amplifier was obviously designed to do just this sort of thing.) The cube speaker sat on top of the rear deck.
This worked better. Not great still, as some of my organ music albums showed, but distinctly better. Acceptably well in fact. Unfortunately the cube slid around back there and banged off the walls. So I took four drywall screws and fixed it to the board.
There. A temporary solution. Like most such temporary solutions, it stayed this way for far too long. That speaker squatted back there like an ugly toad, for something like two years. It got in the way of everything, and also wrecked the `stealthiness' of the stereo installation. But every time I thought about rebuilding the speaker deck I got tired. Plus, this barely-adequate speaker was larger than would fit in the deck without lifting it above its normal height, which would cut into the rear area's already minimal storage abilities. There just wasn't a good solution that I could find. I looked at a lot of car subwoofers, and they were all too large. And I didn't want one of those trunk-killers, in part because they're for a kind of music that isn't mine, and because the trunk is small enough, thank you. I wanted good clean flat response down to whatever I could reasonably get, not screw-loosening thumping.
For even greater unhappiness, the speaker holes under the carpet were starting to show, as the backing-less carpet was sagging into them. I hadn't thought to put some kind of hard support across the holes. The original speaker deck was starting to be pretty unsatisfactory. Not to mention that it was only ever held in place by its own weight, so it could (and did) slide forwards under heavy braking.
Then one day I was pawn-shopping again, and stumbled across a Clarion PSW-160 powered subwoofer that was pretty small and looked like it could be made to fit the car. As an integrated design, it potentially could be very effective for its design. I bought it, for about $100 if I recall correctly. Initial trials showed that it could probably be made to fit under the deck, although not under the deck I had made. (The 6x9's were in the wrong place.) Sound trials showed that it worked about as well as the 12" toad did, so that was acceptible. I doubted that I could do any better than this. However, my life had gotten pretty busy, what with getting married and having a baby, so I sat it on a shelf for a couple of years.
Finally, I got disgusted enough with the situation that I vowed that I wouldn't start driving the car again until I had fixed it up properly. I fabricated a new rear deck and managed to make everything fit under it, so the appearance is still stock. The speaker openings (3) all have wooden `spiders' over them, instead of being open holes. Then I glued some heavy metal screen over that. I used RTV to ensure that the screen wouldn't buzz. I used a cutting torch and an old transmission mount to fabricate a rotating latch to secure the front edge of the deck by clipping to the metal lip that's at the front. This latch was attached to the deck with a tee nut I got out of some VW at the junkyard. The rear edge of the deck was slitted to catch the original metal lip that sticks out at the rear edge of the deck. This new mounting system made the new deck very secure. I had this new deck recovered in the same fabric as before. It looks great!
The PSW works well, probably about as well as the 12" did. (No doubt the 12's box was randomly sized, and not optimal.) The Clarion is ported, and I arranged for the port to fire off an angled deflector, thence out the front edge of the deck. It goes down to about 50Hz, which ain't great, but it's way better than nothing. As before, the electronics are hooked to the factory car alarm, so if it's unplugged it'll go off.
And I am disinclined to screw with it further. There is no doubt that it sounds a lot better than what's in the other convertible, which is a slightly newer Alpine head, stock 4's in front, and some no-name 6x9's in back. It looks good, mounts securely, and is still easily switched over to the rear seating as needed.
I've alternated driving the two SL's, listening to the same CD. (Don Dorsey's Bachbusters, Telarc.) No contest!