E39 Audio: On/Off Switch for the Amp/Subs

The system remote shuts off with the ignition [see: Getting a Remote Signal for the Amp], so I've no worry about getting a flat battery, but it would be nice to have a manual On/Off switch inside the cabin so I can mute the subs while driving if I need to, without having to cut out the rest of the speakers.

While I had the back seats out I ran a wire through the bulkhead into the o/s rear footwell [see: Adding an On/Off Switch], so I got hold of a beacon-switch from a tipper at work to fit inside the cabin. The plan was to run the wires out from the middle of the seat and under the carpet on the transmission-tunnel, then fit the switch inside the armrest-compartment. Neither of these panned out. Running the wires under the carpet is doable, but to lift the carpet [and the sponge backing] up enough involves completely removing the armrest console, as well as all the side trim and clips, so I've taken a shortcut for now and run the wires under the trim below the o/s door, then under the driver's seat and through a gap in the side of the console. The wires are exposed, but they're well hidden and I've made sure to keep them well away from the seat-runners.

As for the placement of the switch, which is over an inch deep with the wire terminals on, it turns out there's just no room for it inside the centre-console. The base of the armrest-console is a solid steel tray with an electronics-module right under it and the storage-tray below the armrest angles up to fit flush with it too. I don't want to go further forward on the dash and mess up the wood so I've fitted it in the storage-slot under the rear air-vents. The plastic slot was missing anyway and the vents were hanging loose, so at least it looks complete now even if it's a pain to reach. Not a problem for people in the back though and that might not be such a bad thing if one is screaming we've missed our turn-off and we can't hear over the drum and bass. I just used a piece of thin plywood for the panel, covered in the leftover vinyl wrap from my ScoobyLab stickers. It's a bit shiny, but the vinyl gives it more of a trim look than black paint.

E39: Amp Swap

With the RCA-feed splitting off the rear-speakers there's no separate controls for the amp on the head-unit. I can turn the Bass up and down in the Tone settings, but its making the rest of the speakers tinny and not lowering the subs enough, so they're just overpowering the sound. They're getting the entire frequency band too, most head-unit sub controls have a lo-pass filter as standard, so I'm getting a lot of unfamiliar hums and wobbles.

My awesome Alpine V12, which matches my Alpine R subs, is a straight mono-block amp and has no controls for volume and filtering either, so I've been forced to make the decision to devolve back to my old, less good Toxic Audio amp. It's not a pretty amp, but it still kicks out 1000w like the Alpine and it has a host more features - 2, 3 or 4 channels with separate volume knobs for each and tunable lo-pass + hi-pass filters. The answer to all my prayers, or so I thought. You can tell the drive of the sound is of a lower quality straight away and it doesn't feel as thumping as the Alpine even turned up loud. The lo-pass filter is also crap and cuts off everything above the low-end rumble, so I've switched it off anyway.

At least the volume of the subs is better matched to the rest of the system now so the speakers are sounding natural again. We'll give it a week while I mess with the settings, but I can't help thinking the Alpine just sounds better. A solution is at hand though - I've found separate sub-crossover units on eBay for less than £10 that have vol. for each channel and great looking filters. It's something else to draw power, but it seems this is the only way left to get this system sounding as good as it could.

E39: Fitted Subs/Amp and kept BMW Head-Unit...

* The Full How-To Guide is on this page: Audio: Wiring Amp/Subs into Standard Head-Unit

The standard BMW Business stereo is a masterpiece and takes up half the dash, but sadly it lacks the RCA-output and remote-signal that are essential when fitting an amp. A fascia-converter is about £10 and a wiring-adaptor about £7, so it's not expensive to throw in any after-market head-unit, but if I do that then I lose my CD-changer, tape-deck and the excellent steering-wheel remote. The cheapest remote-adaptor for Pioneer I can find is £85! and there's no way of knowing if it'll fit my dinosaur model. Worst of all the new fascia would ruin the teutonic look of the dash.

I started checking the forums and found a few people who managed to splice an RCA-cable from the rear-speaker wires, so I thought I'd give it a go. It turned out to be one hell of an involved process. The back seats / parcel shelf have to come out, the speaker-wiring is perplexing and I eventually found a way to get a remote 'on' signal for the amp from a parking-sensor relay. The remote-input on the amp will take any signal up to 12v, so you could just wire it from the battery and have a manual off switch, but at least the fiddlier way means it goes off with the ignition - no flat batteries in the morning. The battery is in the boot too, so there's no need to touch anything up front or run cables under carpets.

The system works brilliantly, there's a LOT of bass there, which I'm quite surprised about with the RCA audio-signal coming off from the rear-speakers, but they are still working fine too. As you can see above, I've also set the subs facing inwards this time so I can make use of the magnificent boot - I'm sure the bass is being stifled a bit this way, the back seats are vibrating like crazy, but it's plenty loud enough either way. The only downside is no separate controls for the subs, so they pump out at the master volume, can't be turned off and receive a completely un-filtered audio-signal - there's some nasty higher frequencies creeping in. My 1000w Alpine V12 amp is a solid mono-block and has no controls either, which is a disaster really because it's the matching unit to my 12" Alpine R subs, but it'll have to make way for a lesser 1k watt Toxic Audio one soon that came with my old Subaru. It's not a pretty amp, but it's got a volume-knob, lo-pass filter to single out the bass and 2 channels, so I can give each sub its own terminal instead of twisting the two wires together. Everything I need basically, but I'll miss that blue-glow screen...

This is where I'd normally put the 'How-To Guide', but the process is too intricate to throw on the wall, so I've given it a page of its own, split into five sections, linked below:

Audio: Wiring Amp/Subs into Standard Head-Unit

Wiring Power / Ground to the Amp
Removing the Rear Seat / Parcel Shelf
Wiring RCA from Rear-Speakers
Getting a Remote Signal for the Amp
Adding an On/Off Switch