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      05-04-2021, 12:53 PM   #1
MTDBassMan
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My odyssey of DIY aftermarket audio installation (F48)

I used to love working on car audio systems when I was a teenager, and it's funny; I was just recently remembering that for the first time in a long time, and pining for the days before car computer systems became inextricably linked to their stereo head units - to the point that it became no longer feasible to replace a factory system with an (much better, more fully featured, more powerful & more audiophilic) aftermarket one.

Anyway, we all know the stock hifi audio in the X1 isn't one of its main selling points. I'm a professional musician by trade, and someone who's very into DIY and audio in general. Those attributes, combined with some free time and a nostalgic desire to venture down another car stereo rabbit hole for the first time in many years, led me to this project!


Discovering the stock "hifi" amp and its super busy wiring harness
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Wires include 4 balanced pairs from head to amp, remote, +12v, ground, and 7 pairs of speaker outs from amp (front doors, front subs, rear doors, center). And I wasn't able to find correct color coding anywhere, and only a pinout of the factory connector harness. So I had to cut and test each wire for continuity with each pin to discover what everything was!! I posted all my findings in a separate post - search under my name to find that info if you're looking, too.
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4 gage power wire connected to the battery positive terminal, via an 80 amp fuse in that clear fuse holder - however I only ran 8 gauge from the fuse to amp (determined by the first amp I was going to use, which ended up being DOA from the manufacturer).
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Testing all those damn wires. Don't worry, the twist on connectors were for testing purposes only. I didn't install things that way - save your flaming.
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I ran a 3.5mm cable from the trunk to the front left of driver glove box for the subwoofer volume remote control, then fed it through a hole I drilled into the back of that glove box insert.
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This is an 8 Ohm, 100 Watt L-pad I bought for the center channel, planning to take the positive terminals of both the front left and front right speaker outputs from the amp and bridge a 3rd channel that only includes common signals on those two channels. I wanted the volume control to be able to find the ideal level, even if that was all the way off, and set and forget it. I was planning on installing in the trunk, but as of yet I haven't actually bothered with it.
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Bought a pair of Polk DB402 speakers for the front doors, left the rear ones stock.
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I also bought a pair of BMW-friendly speaker adaptors for $20 that were a bit larger around the outside of the Polk's frames than I liked, so I filled in that air gap with silicone caulk.
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The stock speakers vs the Polks.
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Polk in the front passenger door, with additional latex caulking between the adaptor and speaker mount, for a more airtight seal.
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Nightmare wiring. But really, kind of fun in its own way. I chose to use male/female bullet connectors to be able to relatively easily switch the factory harness back in someday.
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The Rockford Fosgate 5 channel amp I bought. RX750, or something like that? Running no center as its own channel but potentially tapped from fronts as described above, the 4 doors, and subs as a mono channel and wired in series for a 4 Ohm total load. Frequencies that low are omnidirectional and almost always mixed dead center anyway, so it doesn't make a lot of sense to have separate R and L subs.
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AudioControl DQDX unit attached to the top of the RF amp. These things are really cool! Accepts balanced or unbalanced input, creates a new sub channel from front inputs, has a 7 band EQ for each input pair, its own Linkwitz crossover, an onboard pink noise generator for use with an RTA, and a programming mode that offsets the speaker delay times to optimize the listening position. Basically a DSP unit with much more tactile control than most have. Super cool.
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Cut a notch in the styrofoam bolster piece and ran all speaker wiring through one of the holes in the frame there that the styro piece used, then through a drilled hole in the side of the trunk insert, bundled nicely to amp and EQ.
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And now there's much more bounce to the ounce, and it is good.
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      05-06-2021, 12:38 AM   #2
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Nice documentation dude keep up the great work!

May i ask you where exactly did you ground the amp?
And when you connected the positive wire did you just connect it directly to the terminal or did you use the nuts and bolts around the terminal to connect it more easily

Because I致e noticed that it has all kinds of wires and sensors and I知 too afraid I知 going to trip them or damage them.
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      05-06-2021, 01:12 AM   #3
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Quote:
Originally Posted by Majed View Post
Nice documentation dude keep up the great work!

May i ask you where exactly did you ground the amp?
And when you connected the positive wire did you just connect it directly to the terminal or did you use the nuts and bolts around the terminal to connect it more easily

Because I致e noticed that it has all kinds of wires and sensors and I知 too afraid I知 going to trip them or damage them.
Shoot, I thought I'd uploaded a photo of the grounded lug, but I guess I didn't. It's shown in the 5th photo down - a bolt that's being used up on the sidewall as a ground for some other system already. I used a ring terminal under the nut on that bolt. And for the positive battery connection, I used one of the bolt connections there too, under a nut that was already there.
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      05-06-2021, 01:41 AM   #4
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Quote:
Originally Posted by MTDBassMan View Post
Shoot, I thought I'd uploaded a photo of the grounded lug, but I guess I didn't. It's shown in the 5th photo down - a bolt that's being used up on the sidewall as a ground for some other system already. I used a ring terminal under the nut on that bolt. And for the positive battery connection, I used one of the bolt connections there too, under a nut that was already there.
Is this the ground bolt that you used ?
https://share.icloud.com/photos/0RuZ...HjPQXB9adVyrOQ
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      05-06-2021, 01:44 AM   #5
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Quote:
Originally Posted by Majed View Post
Is this the ground bolt that you used ?
https://share.icloud.com/photos/0RuZ...HjPQXB9adVyrOQ
That's the one!
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      05-06-2021, 08:58 PM   #6
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Quote:
Originally Posted by MTDBassMan View Post
That's the one!
I would have preferred to run a ground wire back to the battery. Possible ground loop can drive me insane.

8 gauge is only good for 40 amps, so the wire may melt before the 80 amp fuse blows. In reality, RMS current draw would be much less anyway.

Given all work and cost, you did not replace the subwoofers? Can the stock subs handle that much power?

Last edited by wcs2229; 05-06-2021 at 09:21 PM..
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      05-06-2021, 09:27 PM   #7
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Quote:
Originally Posted by wcs2229 View Post
I would have preferred to run a ground wire back to the battery. Possible ground loop can drive me insane.

8 gauge is only good for 40 amps, so the wire may melt before the 80 amp fuse blows. In reality, RMS current draw would be much less anyway.

Given all work and cost, you did not replace the subwoofers? Can the stock subs handle that much power?
8 gauge to Class D plays by slightly different rules, and it does just fine. The factory subs are actually great for what they are, but laughably underpowered by the factory amp. It was actually the realization that they could be so much better with more wattage that I devised this specific retrofit plan. If I wanted huge, deep bass, I'd add an add'l powered enclosure, and still may someday. But these days I'm pretty much satisfied with a great sounding "normal" stereo. There's actually only, I think, 150 W RMS going to the two subs together in series, so not a massive amount of power. Still, can't turn the remote knob all the way up and not feel like I could use a little less thump 😉
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      05-10-2021, 08:00 AM   #8
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That's a nice setup!

My door speakers and central speaker have been replaced with coax speakers too, but because of the positioning I'm not really blown away by the soundstage. I guess that's why tweeters are supposed to be mounted higher up.

Did you tune your higher frequencies to compensate the speaker positions? I saw you're not running the central speaker. It can easily make up for the missing high frequencies from the left and right door speakers, but it messes up the soundstage.
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      05-10-2021, 11:03 AM   #9
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Quote:
Originally Posted by Humpus View Post
That's a nice setup!

My door speakers and central speaker have been replaced with coax speakers too, but because of the positioning I'm not really blown away by the soundstage. I guess that's why tweeters are supposed to be mounted higher up.

Did you tune your higher frequencies to compensate the speaker positions? I saw you're not running the central speaker. It can easily make up for the missing high frequencies from the left and right door speakers, but it messes up the soundstage.
You know, at first I had bumped up the higher highs at 8 kHz and bumped 2k a bit as well, and actually cut the central mids at 500, but I've since undone all those changes and put those bands of the EQ for the most part back to flat. I originally wanted Polk DB401 speakers for the front doors, for their pivot-able coax tweeters, but I was sent the DB402 by mistake (and those tweeters have a fixed position). But I've found I'm getting enough high end all the same!

Actually, I meant to update this thread with my findings from running through the time alignment/speaker delay DSP process with the AudioControl DQDX. It's a total game changer. In fact, the way it affects the sound stage and general psychoacoustic effect that had was to effectively "recreate" the center speaker channel! It's pretty cool - it has the ability to use a remote to undo/redo DSP changes at the push of a button, and the new settings are like day and night. And that's as much due to phase cancellations of a good portion of frequency bands as it is to delaying the driver's side audio. The result sounds like punching in a volume boost, EQ correction, and time alignment all in one, but really it's just the alignment that's doing all that; the EQ and volume don't change. So now even with phone calls and parking sensors and such, I feel like the door speakers are absolutely adequate and the center channel is totally unnecessary.

In fact I'm guessing that the center speaker was designed to essentially accomplish all I'm talking about, in a "dumb" way without the use of DSP. Getting the spatial positioning right for the primary listener (driver) just makes all the difference in the world.
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      05-10-2021, 01:49 PM   #10
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I think its DSP that is the biggest game changer...going from basically mush coming out of either door to a soundstage in the center.
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      05-10-2021, 04:30 PM   #11
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Quote:
Originally Posted by allwheelsdriven View Post
I think its DSP that is the biggest game changer...going from basically mush coming out of either door to a soundstage in the center.
I agree. I haven't been able to find a DSP unit as an add-on to the existing amp, only the whole amp with DSP.

The sound also depends on the type of music you listen to and the audio source (FM tends to be heavily processed). I only listen to MP3's on a USB flash drive, which I have adjusted equalization to my liking.
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      05-21-2021, 12:08 PM   #12
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How do you like the Polks and do you have a part number for the adapters?
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      05-21-2021, 12:11 PM   #13
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Quote:
Originally Posted by JJ1796 View Post
How do you like the Polks and do you have a part number for the adapters?
I like them. They're only little 4" drivers, so sadly no option is going to push air like a bigger speaker, but they work well and provide plenty of omnidirectional high end as well.

These are the adaptors I bought: https://www.bimmerhelp.info/product-...eaker-adapters
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      05-21-2021, 02:46 PM   #14
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Nice installation!
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      05-21-2021, 02:49 PM   #15
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Custom Pioneer tweeters and Powered Sub with controls

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      05-21-2021, 02:51 PM   #16
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Sorry can't get the last picture to post properly instead of upside down. It's under the trunk cover and is velcroed to the floor with pro velcro.
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      05-21-2021, 02:52 PM   #17
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Quote:
Originally Posted by Xorbitman View Post
Sorry can't get the last picture to post properly instead of upside down. It's under the trunk cover and is velcroed to the floor with pro velcro.
Very nice!
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      06-08-2021, 11:25 PM   #18
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Hi again, so im planning to install my external sub today, and I知 not that good at wiring (seems like a disaster waiting to happen lol), i got the left panel off the trunk to check for the grounding point for my new subwoofer amp and i saw the one that you pointed out to me, and I saw that it has multiple ground wires for some other electrical systems in the car

My question is that is it ok to ground a 500rms amp to the same bolt that has very thin wires connected to it, I知 scared that it may melt them off or over load them somehow. https://share.icloud.com/photos/0Tz2...rEkrwUE_JGz3rw
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      06-08-2021, 11:37 PM   #19
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Quote:
Originally Posted by Majed View Post
Hi again, so im planning to install my external sub today, and I知 not that good at wiring (seems like a disaster waiting to happen lol), i got the left panel off the trunk to check for the grounding point for my new subwoofer amp and i saw the one that you pointed out to me, and I saw that it has multiple ground wires for some other electrical systems in the car

My question is that is it ok to ground a 500rms amp to the same bolt that has very thin wires connected to it, I知 scared that it may melt them off or over load them somehow. https://share.icloud.com/photos/0Tz2...rEkrwUE_JGz3rw
Nope, for ground it should be fine! That appears to be a solid chassis ground. The amp's ground doesn't really "see" the other wires that may share the same star grounding point, it just sees the near zero resistance path to ground and thus the battery's negative terminal. My amp is similar wattage and it has been just fine.
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      06-09-2021, 10:34 PM   #20
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Quote:
Originally Posted by MTDBassMan View Post
Nope, for ground it should be fine! That appears to be a solid chassis ground. The amp's ground doesn't really "see" the other wires that may share the same star grounding point, it just sees the near zero resistance path to ground and thus the battery's negative terminal. My amp is similar wattage and it has been just fine.
Thank you very much for your helpful information, i did it but sadly it looks like either the rockford amp or the technic harness i got is defective smh I値l try to troubleshoot today hopefully something works by the end of this day
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      06-10-2021, 01:23 AM   #21
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Quote:
Originally Posted by Majed View Post
Thank you very much for your helpful information, i did it but sadly it looks like either the rockford amp or the technic harness i got is defective smh I値l try to troubleshoot today hopefully something works by the end of this day
Lousy! But I feel your pain - I had gone with a Skar amp first, which arrived defective. Hope you get it worked out.
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      06-28-2021, 08:11 PM   #22
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As a recovering musician and long-time car audio guy, I applaud your resolve to DIY.

And really, not meaning to throw any shade here--please don't take it that way! But when I look at the photos of the wiring harness, I think back to your comment here:

"I'm a super hands on electronics and audio guy, well versed in the art of soldering and modification for musical instrument and audio systems, but it seems that the vast majority of threads here for retrofits and component upgrades are focused only on plug and play options. The world of available quality components is so much bigger than just the stuff that gets BMW printed on it!"

And my thought then (and now, especially), is that there's a reason folks go for the Match 7. It's just SOO easy, and it has plenty of power. And it has a sub out.

BMW folks are so incredibly lucky that something like this exists. A plug and play processor/amp with plenty of power and fully DSP abilities at a reasonable price? I've have killed for this in my VW. It takes an $800 unit just to get the Most 150 signal to your processor!

Even for the underseat "subs", 65W is plenty if you cross them at 90 and use a sub.

The Match7 is such an incredible deal for what is can do. Bottom line, I totally applaud your resolve here--but as a fellow audio nut and someone who deals with wires for a living, I'd really suggest that folks just buy a Match7...
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