I found on Crutchfield.com some cheap 6.75 inch Kicker models that the site said fit the rear OB subwoofer position. However, they listed two versions, one with dual 1 ohm voice coils and the other with dual 2 ohm voice coils. I wasn’t sure what the closest match would be for the stock driver (without disassembling the load area side panel first), but I figured the stock amp was unlikely to be set up for 1 ohm speakers. So I ordered the dual 2 ohm version for $79. Crutchfield included at no extra charge: Metra adapter plate (to fit round Kicker driver into oval driver hole); wire harness adapter; and (crucially) detailed instructions for accessing all speakers on the Gen 5 OB. Amazon and other retailers sell the Kicker driver for the same price, but you have to pay extra for the adapter plate and wire harness, and you won’t get the speaker access instructions.
Last weekend I was able to make the upgrade. Removing the side cargo panel was quite involved, but Crutchfield’s instructions were excellent, with descriptions and photos of each step. I removed the panel in about half an hour, part of which was spent finding my bigger ratchet because I couldn’t get enough power with my regular ratchet to undo a 14mm bolt. (I won’t detail the disassembly procedure here because this is Crutchfield information, but you get it for free if you buy a suitable driver from them, or you can order it for only about $10.)
After removing the subwoofer driver, I measured the resistance across its terminals as 4.4 ohms. I won’t go into the whole subject of resistor vs resistor, but suffice it to say that the stock driver is nominally 4 ohms. And it just so happens that dual 2 ohm voice coils, when connected in series, would also be 4 ohms. (If connected in parallel, they would be 1 ohm.) Indeed, when I tested the Kicker wired in series, it measured 4.3 ohms, remarkably close to that of the stock driver. So I was lucky, because that meant the replacement driver would present the same load to the HK amp and not cause it to de-stress or overheat. (The Kicker’s dual 1-oh driver may or may not have caused a problem, but it likely made the amp run a little hotter.)
However, installing the new Kicker subwoofer was not simple. Crutchfield does not provide instructions on how to fit the new driver into the adapter nor the adapter into the car. They don’t even tell you which way to orient the adapter (which is asymmetrical.) I was disappointed to find that the mounting holes in the adapter didn’t line up with all four mounting holes in the stock driver. No matter how I rotated the adapter, the best I could do was to make two of the holes in the adapter line up with the four mounting holes in the car, meaning I would have to drill two holes in each adapter . or the car or both. Additionally, using the two holes in the adapter that lined up, it was clear that I would also need to trim some of the plastic of the adapter to make it sit in the metal mounting area on the car, due to several sections curved adjacent metal.
The first photo attached shows the Kicker driver mounted on the adapter. Neither Kicker nor Crutchfield provided the 8 mounting screws for this, but I had some screws in my box that fit perfectly. I think they were #8 x 3/4”, but I didn’t have them in a labeled package so I don’t know for sure. To fit the 6.75” Kicker driver into the adapter, you need to cut some plastic tabs inside the adapter, which I did quickly with a Dremel tool.
In the photo, the red ovals along the top left and right show where I cut the pieces on the outside of the adapter. After test fitting this mount to the car, I decided I needed to trim a bit more of the plastic in the oval screw hole on the top right. (What you see here is not the final version.) The red arrow in the photo is where I drilled an extra hole in the adapter I used to screw that corner into the car because after cutting it wouldn’t fit. there should be enough plastic left around one of the other two holes in that corner of the adapter.
Looking at the first picture, the two holes in the bottom half of the adapter fit into the stock holes in the metal mounting area of the car using threaded bolts. However, I had to drill two holes in the sheet metal mounting area for the round hole in the upper left and the new hole (red arrow) in the upper right. The second picture below shows when I was test fitting the mount on the car to mark where those holes would go. (This is not the final installation, as there are no screws holding the top of the adapter to the car yet.) If you are going to do this, be careful when drilling the top right hole because there is limited depth behind that area before the drill your hitting another metal part.
I used two #12 x 3/4” stout sheet metal screws to attach the top of the adapter plate to the car.
The wiring harness that Crutchfield offers has slider connectors on one end (and the Subaru connector on the other), but the Kicker driver only has bare wire terminals. So I removed those slide connectors, removed the wires, and repaired the exposed copper using a soldering iron so it wouldn’t oxidize from sitting for years inside the car. I also made a jumper wire to connect the two voice coils in series. (The instructions with the Kicker speaker illustrate how to wire the 4 driver terminals.) I drilled a small hole in the side of the plastic adapter to put the wires through and covered it with a rubber grommet.
The last thing I did before permanently mounting the mount to the car was to apply foam putty along the contact surfaces of the back of the adapter plate so it would lock in place and not squeak.
With the Kicker subwoofer mounted in the car and all wired up, of course the big question is: How does it sound?
