# Subwoofer add-on: RCA outs from 2000 540i w/ DSP



## djcwardog (Jan 30, 2005)

Folks,

I ran a search here and didn't find any old posts, so...

I'm the guy who posted about adding a Blitzsafe adapter to run an Alpine CD changer and get an auxillary input on my factory DSP system. That all works great, especially with my Delphi SkyFi2 XM radio setup.

I see on the web where Bavarian Autosport sells a proprietary harness to use in a kit with an add-on subwoofer with built-in amp. I want just the harness but they say they don't sell that way. I have an Alpine MRD-M500 sub amp and a JL Audio 10" driver in a box that fits in the trunk. I want to tap into the stock wiring and add this onto the existing stock sub setup (two 6" drivers I believe). The existing subs do better than I would have thought, but I think adding this in will give that last octave I crave! I could also splice into one of the sub speaker wires and do speaker-level trick, but I prefer the line level if possible. I don't know the wiring diagram for this system so I am hesitant to just splice in... I do have the two-volume factory service manuals.

Help?


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## AsianImage (Oct 10, 2004)

Here is my install. My installer used the stock sub wires right into my amp, stock power, stock acc, stock everything. He spliced into all the factory wires with ZERO problems.

Here is the thread...
Bazooka install


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## el_duderino (Aug 1, 2005)

As I understand DSP systems, your HU sends a fixed-level signal to the amp and the only way that the volume changes when you turn the knob is that there is an i-bus data line that tells the DSP amp to get louder or softer.

So if you want to retain the DSP amp, you NEED to use those speaker wires.

Read these:

http://www.x5world.com/showthread.php?t=3896

http://www.x5world.com/showthread.php?t=5369


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## djcwardog (Jan 30, 2005)

*tap into stock speaker (sub) wires*

If I follow the posts correctly, I can just wiretap a stereo pair of speaker wire leads running into either of my stock sub speakers under the rear deck. They obviously have variable gain to go along with the other speakers in the car when the volume is adjusted. I just checked my amp - preamp level inputs only! I'll need to use a speaker level to preamp (RCA) level converter.


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## el_duderino (Aug 1, 2005)

djcwardog said:


> If I follow the posts correctly, I can just wiretap a stereo pair of speaker wire leads running into either of my stock sub speakers under the rear deck. They obviously have variable gain to go along with the other speakers in the car when the volume is adjusted. I just checked my amp - preamp level inputs only! I'll need to use a speaker level to preamp (RCA) level converter.


What kind of amp is it?


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## djcwardog (Jan 30, 2005)

Alpine MRD-M500


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## el_duderino (Aug 1, 2005)

That amp is spec'd to take 8.5V in, so I'd see if you can run it without an LOC and just with speaker wires with RCA ends on them.


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## djcwardog (Jan 30, 2005)

If I understand correctly, I can just take an RCA cable, cut the connectors off of one end and then splice those leads into the stereo pair of wires going from the trunk amp to the stock subs under the rear deck. Getting battery power and ground to the amp from the trunk-mounted battery is easy - what about an amp turn-on splice? One of the 18 wires on that main harness coming off the amp? I just saw your reply to the post about the custom sub box for E39 cars for $200 - replaces the battery door in the right-rear of the trunk. Is that the easiest way to use my 10" JL sub or are there other custom boxes out there? I would just add this on and let the stock subs keep playing - set my amp to handle the lowest bass and flatten the stock system off to reduce the pressure on the stock subs.

Thanks!


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## tecasur (Nov 16, 2005)

*bmw custom subwoofer box*

where can I find this custom subwoofer box for E39 cars for $200 which replaces the battery door in the right-rear of the trunk. I am thinking of having one made at Car Toys but it is quite pricey.

Thanks.

Anthony


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## skylineg35x (Nov 12, 2005)

el_duderino said:


> That amp is spec'd to take 8.5V in, so I'd see if you can run it without an LOC and just with speaker wires with RCA ends on them.


El Duderino, what the hell are u doing here? Aint you in the G35driver forum?


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## djcwardog (Jan 30, 2005)

tecasur said:


> where can I find this custom subwoofer box for E39 cars for $200 which replaces the battery door in the right-rear of the trunk. I am thinking of having one made at Car Toys but it is quite pricey.
> 
> Thanks.
> 
> Anthony


Anthony,

Look here for the bimmerbox.e39:

http://www.theunder.com/underaudio/

I still have not made up my mind as to what to do, and I still question how to get the amp to turn on... If you buy one, let us know...

Thanks,

DJC


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## underaudio (Mar 24, 2006)

hey folx. updated link for the bimmerbox is here:

http://www.underaudio.com

as for how to get RCA outs, in a nutshell, it can be done in a number of ways. but for most aftermarket amps, all you need is an LOC (line output converter) to convert the ballanced audio to un-ballanced, and convert speaker level outputs to line-level.

i have posted some notes aout how i set my system up along with some suggestion for alternate configurations if you don't want to replace the factory amp (although i recommend it, especially if you have the DSP - yuk).

http://www.underaudio.com/products.htm

hopefully you will find this helpful - and let me know if you have any Q's about the bimmerbox.

oh yeah - the amp turn-on: if you check http://www.bmwtips.com you can find the pin-outs to the harness feeding the factory amps in the trunk. you just need to use the power-on lead in the trunk.

please excuse the website - i'm a music dood, not a web dood


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## el_duderino (Aug 1, 2005)

Underaudio, I have to disagree with you. I know a lot of installers will use any old LOC on balanced outputs, but a lot of installers are just plain wrong. 

Many amps don't need one at all. If you do use one, I recommend using a balanced-specific unit like the Soundgate LOCPREA for best results. 

But many amps don't need one at all.


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## underaudio (Mar 24, 2006)

el_duderino

we really are not disagreeing. it boils down to the specs of the equipment you are adding. if it accepts unbalanced audio, you don't need an LOC. if it does not, like most of the stuff on the market, you need one.

from personal experience, i tried it without one and had "strange" results. if the RCA shield touched the chassis of the elecro-xover - eek. balance/fader didn't work and freq. repsonce was "odd" to say the least.

once i added the sven4, - a brand new world of pristine audio. go figure. that is pulling 4 channels direct from the HU. 

all i can say is check your specs and if you add an LOC - make sure it is like the sven4 and does the ballance conversion properlly. there is a long thread somewhere that gets into the technical reasons why.

we are really on the same page.


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## underaudio (Mar 24, 2006)

i wanted to add that you touched on the real issue -

most installers don't know much about the BMW setup. its left up to the customer to do the research to get good results.
just like you said, they may throw any old LOC in your car when you really need a special one.


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## R1150RS (Jul 1, 2006)

*What's the missing converter?*

Hi folks,
I'm adding (well, have added) the nokia subwoofer box to my non-dsp system, driven by an alpine mono amp.

What I would LIKE to do, in an ideal world, is tap into the inputs to the factory amp, run them through a crossover, then send the mids and highs back to the factory amp, and send the lows to the alpine amp for the sub. As you all know (and I found out the hard way - because I didn't read all the forums FIRST), the inputs to the factory amp are NOT line-level, they're balanced differential... That means I need an LOC between the head unit and the xover. But that leaves me with LL to send back to the factory amp... I can't send line-level back to the factory amp...

I tried an experiment last night to confirm this. Threw together a setup using a 'normal' head unit, my xover, and a bunch of RCA cables in my trunk, and tried to feed the line level inputs to my e39's amp.. and... I had to crank the aftermarket head unit up all the way to get a line level signal high enough to make the factory amp produce output that I could easily hear from my stool next to the trunk... I.e., 'all the way up' produced output that wasn't even 'halfway up'.

So, my idea is: I need something to convert the crossover output back to the higher level, balanced diff inputs the amp is expecting. Well, actually, I suspect that the amp will take non-floating ground inputs, but they need to be cranked up to the ~6vp-p that it's expecting, not the 1 or 2 vp-p that the crossover seems to be putting out.

Do any of you know of a converter to handle that side of things? I know the sven4 (or similar) will convert from balanced diff to line-level. I need something to do the reverse. Or another idea.

The whole point is I don't want to send those low freqs to the factory speakers. They don't reproduce them well, and it just 'muddies' up the sound by allowing them to reach the speakers.

I know many people here just set up their LOCs on the speaker level outputs from the factory amps, but I'm not satisfied with that approach because it doesn't allow me to 'remove' the low freqs from the signals that the factory speakers are reproducing.

Any ideas? On either the gizmo I'm looking for, or some completly different tack to take? Right now, the only idea I have is to replace the factory amp with an aftermarket amp desinged for LL inputs, but that will lead to replacing the speakers, which also implies giving up the mid level speaker in the front doors. And which will cost $$$$, and require lots of installation effort. 

Thanks for any ideas or help or corrections


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## el_duderino (Aug 1, 2005)

The gizmo you are looking for (I hesitate to say "that you need" because I am not sanguine about your eventual results) is a Peripheral SVEN. It will go RCA to balanced OR balanced to single ended RCA.

http://www.cardomain.com/item/PERSVEN2


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## R1150RS (Jul 1, 2006)

*Boy, do I feel silly...*

Thanks for pointing that device out. I feel rather silly because the device I mentioned in my original post (the SVEN4) is just like it, but 4 channels. I just didn't catch that bit about it being able to go both directions - thought it was strictly a 'speaker level to line level' gizmo.

Thanks, again.

However... You mention you're not exactly sanguine with the eventual results. As you've been down this path already (or rather, a similar one), I'd value your elaboration on that point. Is it because you think I'll be introducing too much noise? Not confident it will work as I'm envisioning? Something else entirely?

Thanks


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## el_duderino (Aug 1, 2005)

The electronics could work OK, not certain about that (if any noise is present, the woofer woudn't play it but the mids and tweets very well might - why I don't do this kind of installation at our shop even though we do OEM HU-retention installations all the time). 

But I don't think there's any way to make that nokia underdeck sub sound good.


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## R1150RS (Jul 1, 2006)

*Underdeck sub sounding good.*

Ah... 
Yes. I hear you on that one. The only reason I'm trying this is because I wanted an easy install that would look stock and clean (clean being more important). But I'm with you on that uncertainty. So far I'm not too impressed. In general, I think bandpass enclosures suck - this one is reminding me of that. Very boomy around certain freqs. Anyway, I'm withholding final judgement until I can get the signals cleaned up.

I wouldn't be surprised if I end up putting in an aftermarket sub or two. Looks like the consensus on the forum is to put in something in an enclosure, but I'm also considering some free air subs mounted to the rear deck. Some people have expressed concern over rattling there, however. I'm also worried that since I have the folding rear seat, that solution just won't work well at all (trunk isn't even close to being sealed). I think the ideal (for me) would be some 8"s or 10"s mounted under the rear deck into an enclosure that cosmetically resembles the Nokia box.

In the meantime, I've ordered a couple of the SVEN4s, and I'll post a follow up after I get them installed.

Thanks


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