E60 Audio: Getting a Bass RCA (Audio) feed from the Stock-Subs.

If you want an aftermarket amp + subs in the boot then you need an RCA-feed and tapping into the rear speaker-wires does not work on the E60 and other iDrive BMWs as it does on the E39, E46 etc. All US E60s and others with factory-upgraded sound-systems have two subs under the front seats run by a stock-amp in the boot, on the left-hand suspension turret behind the panel. If you have this see this guide on //// to tap into the wires on the stock-amp.

Most non-US cars don't have a built-in amplifier in the boot, but they still have subwoofers under the front seats. These are driven by the head-unit and the EQ sends a different set of frequencies to each set of speakers. [See: http://musicarnw.com/bmw-factory-audio-explained/]. The rear speakers are only 4" so they don't get much low-end at all. To get proper bass it's worth going the extra mile and running cables all the way to the stock-subs, which get the real low-range frequencies.

** NB: This is to fit subwoofers on a bass-only channel. If you are fitting component speakers or 6x9s then you will need a broader range of frequencies and are better to tap the rear speaker-wires, covered in THIS POST, which is a lot easier. **

PROCESS:

Getting to the sub-wires is quite involved, but not difficult if you have the right tools. There is a + and - wire to each sub, so two new speaker-wires will need running either side. I used one length of twin-core 1.5mm wire on each sub, about 6 feet of wire is plenty.

1. Slide the seat all the way back and remove the plastic caps from the front of the runners.

2. Remove the two bolts from the front of the runners using a T50 Torx-head wrench.

3. Slide the seat all the way forward and remove the two bolts holding the rear of the runners using a T50 Torx-head wrench.

4. Lift the seat up. tilt it back out of the way and prop it up.

5. Remove the four crosshead screws from the plastic-grille above the sub and lift it off.

6. Move the carpet on the door-sill out of the way and cut the fabric-tape binding the wires going to the sub together so they can be pulled apart.

7. Splice your new speaker-wires into the wires going to the sub as pictured below. O/S - Red/Blue for [+] and White/Brown for [-]. N/S - Red/White [+] and Brown/Yellow [-]. [Soldering would be the best way, but I just went for the quick and easy Scotch-lock way again].

8. Run the new speaker-wires out from under the carpet and
along underneath the door-sill trim, up the side of the back seat and along the top of the back seat to the middle.

9. Lower the centre arm-rest and remove the plastic-trim panel from behind it by pulling out the two push-clips from the lower edge and working it off.

10. Thread the new speaker-wires down behind the back-seat at the centre. Be sure to thread the wires just behind the seat-back, but not down against the parcel-shelf, which ends at an annoying ledge. If you see the wire passing down behind the small round hole near the top of the seat-back behind the arm-rest then your on the right route.

11. Inside the boot the new speaker-wires should be seen poking down into the boot, or if it isn't you should be able to reach under the lip at the back of the boot and pull it down.

12. Install the four wires to your amplifier either directly by adding red/white RCA-type connectors to them, or via a crossover-box, which is the better method. Fitting a crossover is covered in THIS POST.