There are two primary problems to be overcome when installing a good speaker system in the rear of the Audi Coupe. The first is the vertical gasoline tank behind the back seat, which prevents the use of subwoofers mounted so as to fire through the rear seat cushion. The second is the flimsy cardboard parcel shelf to which the stock speakers are mounted. The first problem is intractable - you are not about to relocate the gas tank in this car! It means you have to find some other satisfactory solution to mounting some sturdy low frequency drivers. The second problem has a fairly intensive but elegant solution. Several of us have discovered that the Audi Coupe has a 3/4" wide groove in the sheet metal, horizontally running just below the rear window and forward at the base of each "C" pillar. What I have done is: Rip out the silly cardboard thing. (save it for possible resale situations) Starting with a piece of cardboard that is too big, slowly cut it down to make a template for a board to fit into this groove. It isn’t quite straight across the back, and the sides are not parallel. Your front edge will, however, be a straight line. When you are satisfied that your template is just right or perhaps 1/16"-1/8" too big in a few places, use it to mark out and cut a piece of 3/4" plywood. This board will now be fitted to the grooves in the car’s body. The reason the template should have been slightly too large is to facilitate the next step - shaving down the board until it is just right. When just right it hardly even needs to be screwed in place, but this will be done. Now you need a vertical piece for the front. This will be attached to the little indent that crosses the sheet metal behind the top of the rear seat back. Whatever type of joint you are happiest making should be allowed for at the 90 degree meeting of the front board and the top, or "baffle" board. One tricky part is the outer front corners of each piece. They need to be cut carefully and rounded (in cross section) to allow free movement of the seat belts. A few small pieces will be required (vertically) to seal up this gap. I curved the ends of the front board, a 90 degree segment of a circle, and cut down some cardboard tubing to fit in the space neatly. Flat material could also be fitted to a curved edge here. This board assembly will be cut with holes to fit your speakers, painted, covered with cloth, fake fur, or leather, caulked fairly heavily and screwed into place. (I actually put "speaker fur" on mine with spray contact cement after installation, trimming the edges with a sharp knife. If you do this watch for overspray on the rear window!) You will have to be creative with screw and bracket locations. JUST DON’T DRILL OR SCREW INTO THE GAS TANK! The caulk not only seals the enclosure you are building but minimizes squeaks and rattles from the joint between the sheet metal, which flexes a little while driving, and the plywood. You will want to stuff the space between the board and the sheet metal with fiberglass or polyester wadding or dense open cell foam. I cut a bit of the sheet metal below the parcel shelf out, trying not to remove what looked like it was needed for strength. This was so the bass speakers would be better able to utilize the entire trunk as an enclosure. As far as speakers go, you want to build the best sounding full range system into this board that you can arrange. I am partial to using home speakers in the car - in fact when I haven’t yet built the stereo in my car I usually just seatbelt a couple into the back seat. Your choice will depend on the amount of volume you want, the amount of power you will have, and what you already own. My philosophy here is to use more power than you will ever use (so you don’t break your amplifier(s)) and then build the speakers to handle more than that. It’s a lot of work installing a nice car stereo - you don't want to spend a lot of time replacing broken bits. I would suggest three levels of rear speaker capability, based on what I make. The first, practical for 25 - 75 watt systems, would be a six inch woofer and 1" aluminum dome tweeter on each side. The second, for say 50 - 150 watts, would be an eight inch woofer and the same tweeter on each side. Thirdly, and approximately what I have, for 100 - 300 watts would be two eight inch woofers (PRO 006), one midrange, and one tweeter on each side. I wound up using a pair of very efficient (and expensive) 12" drivers I already owned, running off 120 watts each side, and a six inch woofer plus tweeter combination, from 120 Hz up, driven by 60 watts on each side. I then have the same six inch/tweeter combo in the front of the doors driven by another 60 watts. The power comes from a pair of Yamaha YPA-1000 amplifiers - each one gets the front and rear signal from one side only, and then splits them into three channels. The amps, I suppose, think they are seeing stereo, but each one only deals with one side of the system. This should minimise cross talk. If I had not already owned the 12" drivers I would have used the two eights, one mid and one tweeter arrangement. This is a great sounding system, the same drivers as are in the HUMAN 88-41, which handles about 300 watts, and goes from the mid twenties on up to 26 kHz. I have mounted a 1/2" plywood board vertically right behind the gas tank to hold my amplifiers, attached with 90 degree brackets and sheet metal screws to the metal below the parcel shelf and the two frame rails that break up the trunk space. If the amplifier(s) are bolted to this board, it is bolted to the brackets, and the sheet metal screws are mounted so as to be obstructed by the board, no casual thief can make off with your amplifiers. They must at least dig up a few different wrenches and spend the better part of an hour upside down in your trunk. Quite a deterrent. You can make it even more difficult for them by using at least two bolt sizes! See more about the speakers I build at the HUMAN Speakers web site |
