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BMW 3-Series and 4-Series Forum (F30 / F32) | F30POST > Technical Forums > F30 DIYs and Coding Discussions > DIY sub install on BMW "STEREO" systems
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      08-16-2013, 12:29 PM   #1
1lyfe's Avatar

Drives: AW F30 328i Xdrive
Join Date: Jan 2012
Location: Toronto

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DIY sub install on BMW "STEREO" systems

So if anyone here has the base stereo system (4 speakers no center no subs) you will notice your speakers are absolute garbage. IMO the bass is lacking, the mids are acceptable and the highs are overpowered.

The learning process:
(Im writing this section because i've spent the past week diagnosing whats wrong with my system so maybe it will answer some of your questions too if you encounter problems during install)

So i've wired up subs and amps into stock head units before and it is always very straightforward. Tap into one of the speaker outputs (or two if you have a 2 channel amp) and drag that wire into an LOC and from that RCA into your amp and out to your sub. But for my F30 it wasnt that straight forward (it could have been my equipment since it was relatively cheap). When i wired it all up and turn on the system i found that the sub was not very loud, like its on but its very very weak (you had to turn the bass in idrive to max to even get it to audible levels). Everything looked like it was hooked up properly so i decided to take it into a car audio shop and have them check it out if i did anything wrong and they concluded everything was wired correctly but my amp was too weak (it was an old 100w amp and a 100w sub). So fine i went and bought a 300w amp with a 300w kicker sub, plugged it in......and it had the same problem.
I spent the next following days buying a whole bunch of stuff to try and make it work ie: rca pre amp line drivers, better amps and subs. no dice. Then i decided to get a crossover...AND IT WORKED!
i mean i dont know why it would make a difference (since my amp has a built in crossover) but adding this separate one makes the amp work like how it should be.

The install
Step 1:
Pry off the trim that goes on top of the climate control and there's two plugs behind it, pull it off.

Step 2:
fit your finger underneath the climate control at the bottom and gently push down, this panel will just unclip without much effort.

Step 3:
There are 4 screws, one at each corner of the climate controls (i cant remember the exact size but i just got an allan key that fits and used it).
Unplug the cable thats behind this panel (its very tough to get out the first time) This is a bad picture but iots the cable on the right.

Step 4:
There are 2 screws holding the head unit in place, unscrew them and pull it out. At the back of the head unit there is a big square-ish looking connecter, there's a latch holding it in, unlatch it and pull it out.
This is where you will be tapping the wires into.
White/Red and White/Brown (rear left +/-)
Grey/Red and Grey/Brown (rear right +/-)

Step 5:
Take all the wires and feed them through one of the many holes that goes towards the passenger glove box. To get to this wire, there are two 10mm hex bolts that hold the panel under the glove box. Take that off and you can reach all your wires. (i forgot to take a picture of this but this is what i have)

Step 6:
Wire it out towards the door and slip it under the weather strip w.e you call it and wire it along the side until you get to the back seats

Step 7:
Pull up on the bottom portion of the seat and you can feed the wire through to the trunk. I highly recommend you do not pull the entire seat out because i did this and getting the seat belt buckles to go through the holes is the biggest pain the the ass ever.

Step 8:
Get an amp kit from a local store (i got 8 gauge but 4 gauge is even better)
Wire the positive and negative straight to your battery and hide the wire under the carpet liner.

Step 9:
I wanted my amp to be out of sight so i put it in the compartment that goes underneath the trunk floor. I cut a little opening to feed all my cables through so the board sint raised on one side compared to other.

Step 10:
Wire everything up. This is how i wired mine up:
wires from head unit -> crossover -> rca input on the amp -> sub

for the "remote" input on the amp and crossover i tapped into the fuse box in the trunk since everything in there turns on when you unlock the doors.
I used something called add a circuit which looks like this:

Step 11: hook up the sub!
i wanted my sub as small as i could get so i didnt have to compromise much trunk space, this kicker sub i found was just what i was looking for, very thin but still has a lot of bass. i put it up against the back of my rear seats and used strings to keep it from falling backwards or sliding left and right when i corner (yes its shoelace im cheap until i find a better replacement haha

Thats it you're done!
adjust the bass on the amp/crossover as needed
for me im waiting for another amp and im going to use the high end frequency of the crossover and wire it to oem speakers.

Some notes

The cabin is very insulated so the sub in the trunk is very quiet. the gain on my sub is set to the max and you have to set the bass pretty high on your idrive to hear it.
the problem with this is that your speakers will most likely drown out the bass coming from the trunk so thats the reason i got the crossover.
Im going to get a second amp to wire the rest of my speakers to so i can limit the bass coming from them in order to hear the bass coming from the trunk.
Current Mods: JB4 , H&R Rear Sway bar, Ultra Racing Strut Bar , 19" M5 Reps Staggered , NBT retrofit , JBL MS8 Amp and 10" Sub
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      05-22-2014, 05:58 AM   #2
Private First Class

Drives: 2012 BMW F30 320d SportLine
Join Date: Sep 2013
Location: Norge

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I was planning on doing this in my car -> http://www.bimmerfest.com/forums/sho...d.php?t=732603

But after I recived my amp and was ready to hook it up, I found that I dont have any factory amp. I thought I had the HiFi-stereo, but I have the same as you.

Do you have any suggestions on how I could hook up my JL Audio XD700/5 amp to my car? I want to be able to hook up all the speakers.

Last edited by Sleepwalker; 05-22-2014 at 09:05 AM.
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      12-06-2014, 09:39 AM   #3
F30 SA

Drives: 2013 320i Modern Line
Join Date: Jun 2013
Location: Durban, RSA

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Excellent write up.
Also been chasing my tail for 20 months. really strugling with setting up my system.
Did find out that the signals to rears are already processed to exclude very low signals for bass. Probably why yr sub was so soft.
I have the SWS 8x under both seats, Alpine G 4"coaxial in all doors but amplified infront only. Alpine 5 channel amp MRX-v70.
The fronts are high passed on 180Hz and Underseats are low passed @ 120 HZ. Gains are all at around 20%. At high volume the Underseats seem to bottom out. They are connected in parallel.

Any ideas for improving the tin sound quality wud be most welcome.
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