I have been thinking about a subwoofer add-on for a little while now. I have the Harmon Kardon system, and even though the low end isn’t too bad, I have been getting more and more rattling in the passenger’s side front door, apparently a common problem. I started looking into small under-seat subwoofers and tube-style subs, and what would be needed to wire them up. Then I came across Bhom’s sales post in which he had a wiring harness he made for his sub amp for sale. After talking to him about it he asked if I would want to buy his amp + sub + harness altogether and I lept at the chance. I quickly got the dimensions for the subwoofer box and made a cardboard stand-in for it to make sure it would actually fit under the false floor in the trunk of my V60. The sub is an Alpine SBR-S8-4 and it JUST fits, with some very minor modifications. The amplifier is an Alpine MRV-M250 and fits nicely into the little hidey-hole on the left side of the trunk directly behind the wheel arch.
In order to fit the SBR-S8-4 subwoofer under the false floor in the V60 you must remove the decorative ring around the speaker grill, place it with the speaker facing down, and rotated so that the “wider” side of the box is facing the rear of the car.
This allows the speaker grill to rest against the “muffler hump” with the grill in the deeper part of the trunk just forward of the “muffler hump”. Also, you will need to take a rubber / deadblow hammer and dent down the spots where the corners of the subwoofer touch on the forward edge of the “deeper” part of the trunk, you only need a few extra millimeters of space to get the false floor to close flush.
You can easily get power for the amp from the fuse box on the left side of the trunk. Depending on the year and car packages you have, you may have the unused trailer circuit available, or you can tap off of the (4) 30 amp fuse row. The 4th slot in the 30A row was open for me and I used a spade connector to attach to the “hot” side of the fuse box from underneath. No need for an add-a-fuse or anything, the spade connector fit snugly into the bottom of the fuse box where the hot connectors are. I ended up using the grounding point that is under the plastic lip of the trunk area all the way at the back left of the trunk. I had to extend the ground wire that came from Bhom’s system, but it makes moving and messing with the amp easier than when I initially had it attached to the grounding point under the rear left seat.
Now onto wiring the speaker inputs and remote signal wire. First off, you are going to need to remove a bunch of trim pieces. First, remove the kick panel under the glove box, which requires a T25 torx bit and unplugging the footwell light, then pull off the passenger’s door still trim, then the passenger’s dashboard end cap, then the curved piece that goes up in front of the front passenger’s door, between the door sill trim and up to where the headliner starts, lastly, the passenger’s center tunnel side trim. You need to remove these pieces so that you can pull back the carpet in the passenger’s footwell to run your remote signal cable from the switched 12v sockets.
Next, remove the rear bench seat via the 2 clips on the outside edge of the bench. Just push in and slightly down with a flathead screwdriver and pull up on the seat. It is easy once you get the flathead on the actual clip mechanism, but it does take a good amount of pushing and pulling force. After the bench is out of the way, you can remove the plastic door sill trim on the rear passenger’s side, and lastly, the passenger’s side bolster under the seatbelt by prying it out from the top, then lifting up and away.
I added some additional 12v sockets that will live behind the center waterfall console in the near future, so I already had a wiretap on the switched 12v line, the thicker green/orange cable on the passenger’s side of the center tunnel. Tapping this line is the easiest and cleanest way to get a remote signal for an amplifier. However, when locking the car the switched 12v power comes on for about 10-15 seconds before turning off again. Just something to keep in mind.
After you connect your remote wire to the switched 12v, you can pull back the carpet all the way to the front of the passenger’s seat. I fed the remote wire behind the black plastic air ducts that run vertically in the above picture, then ran the wire under the carpet along the air vents, where they go under the passenger seat. The cable then runs straight over to the door sill, in front of the passenger’s seat. The remote wire then meets up with all the wiring running towards the back of the car.
Hook up your wiring harness with amp wires, run the wires underneath the passenger’s seat, and into the little groove where the front and rear pieces of the carpet overlap.
Fish the cable between the pieces of carpet and it will be at the same spot where you have your remote wire. I also had a subwoofer knob, which I placed behind the waterfall console and I ran the wire down to where the remote wire splice was, then followed the same path. With all of your wires ready to go to the trunk, start by fishing the wires under the edge of the plastic trim on the B pillar. All 3 of my cables easily slid under the edge between the plastic trim and the carpet. Once you are past the B pillar trim, you will either need to cut the carpet, or feed all the cables through the “slot” in the carpet so that they do not obstruct the rear door sill trim clip. I pushed the cables through the “slot” so that they all go down into the void where the factory wiring harness is coming up from a lower depth and into a plastic cable tray. Then route the cables into the plastic cable tray.
Now you can simply follow all the wires that are heading into the trunk.
Next, you will need to remove the false floor in the trunk and the fiberglass insert. Pull back the insulation and you can see where the wires come into the trunk on the passenger’s side. Run your cables underneath the insulation, just in front of the trunk wireless key sense module.
You can see where I tucked the amp in, just behind the driver’s side rear seat. It is the perfect size for the Alpine amp and I stuck it down with adhesive velcro. I also used adhesive velcro to hold the subwoofer in place.
IMPRESSIONS
The sub can hit pretty hard, but not insanely low, its real beauty is how well it blends with the system under normal volume. If you crank it way up you will quickly find that it plateaus in volume, but still very loud and tight. Luckily, almost nothing rattles when I really push it, but there are definitely a few rocks trapped behind the muffler heatshield that I can hear rattling around from outside the car. Inside the car, there are no rattles. I turned down the 60hz frequency in radio to 2 clicks above the minimum, which has eliminated the rattling in the passenger’s door and acts as a low pass filter for everything but the subwoofer. I boosted the 200hz a little to give a little more midbass oompf to the door speakers since my subwoofer is currently set to ~90hz cutoff. For daily listening I have the amplifier gain set at nominal, “bass boost” set to +4 to compensate for the lowered 60hz from the radio, and the remote knob set to just under halfway. I can easily crank it for songs with the knob placed behind the center console, used Tessa tape, and it’s holding up to the summer heat so far. The installation was surprisingly easy, aside from ultimately needing to run the switched 12v line and one weird issue that seems to be coming from the amplifier itself. If I try to set the gain above nominal the sub will start humming at like 60hz when you lock the car and gets extremely loud. The biggest part of the job would be finding the correct harness and splicing it up, which I did not have to do since I bought this as an already complete and functional system.