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BMW 3-Series and 4-Series Forum (F30 / F32) | F30POST > Technical Forums > Navigation, iDrive, Audio, Video, Bluetooth, Phone, Cameras, Electronics > DIY major HiFi upgrade for under $1,000!
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      11-06-2013, 02:07 PM   #1

Drives: Blue 2014 335i M Sport, Manual
Join Date: Nov 2013
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DIY major HiFi upgrade for under $1,000!

This post (also posted on my blog) outlines a DIY stereo system upgrade for an F30 - 3 series equipped with the standard HiFi system.
After doing a little research and specifically reading this post, I set out to do my own upgrade. Just to clarify, I do have some experience installing car stereos and building speaker boxes so none of this was new to me, but if you follow this guidance, I'm sure a novice could pull it off. I'm going to break this post up into the following 4 sections for ease of navigation: The Plan; The Box; The Install and Tuning. Your specific needs may dictate which sections are more important to you but they're all here for your reference. So here goes:

The Plan…....
I didn't want to break the bank on this so I set my budget to $1,000. As it turns out I managed to do it all for just under $700. I achieved this with a little help from Amazon (for amp and parts) and Craigslist for a second hand subwoofer. My plan was to replace the factory amp with a clean 5 channel Class D amplifier. I needed 5 channels because I wanted to send the high pass signal (above 200hz) to the 4 inch factory door speakers. Send a band pass signal (between 80hz - 200hz) to the factory under-seat woofers, and still have a subwoofer channel (below 80hz) to send to the a true subwoofer in the trunk.
This is what I ended up buying…....
1 – Wiring Harness (via Technic on this Forum) $90 PM Technic
1 – JL Audio XD700/5 (5 Channel Amplifier with built in crossover) $419 Amazon
1 – JL Audio 12w3v3-2 (12 inch 2 ohm subwoofer) - $75 second hand via Craigslist
1 – JL Audio HD-RLC – (Remote level control for subwoofer output) $29 Amazon
¾ inch MDF, Carpet, Adhesive, Glue, Silicone, etc. - $70 Home Depot / Amazon

The Box…....
So, I wanted true sub bass but didn't want to sacrifice too much space and needed to stay within budget. I search for a while and settled on the JL Audio 12w3v3-2. It's a high performance 2 ohm subwoofer that has good power handling (perfectly matched with the XD700/5 mono output), and only requires 1.25cu/ft of volume in a sealed enclosure. After measuring my trunk and building a couple templates, I managed to come up with a rear-firing wedge shaped design that fits snug against the back seat and takes up minimal trunk depth. Below is the detailed spec as well as some pictures of the whole process .

Started by taking measurements of the trunk and doing a detailed spec to ensure volume and displacement requirements were being met .

Then cut a cardboard template to ensure proper fit of the proposed design.

Then built a wooden frame to get exact piece sizes and cut angles.

Next bought the wood (3/4 inch MDF) from home depot and had most of the pieces pre-cut to save time.

Cut the angles and end pieces, wood glued / nailed (and screwed) all the pieces together to make the box.

Once dry, cut out a hole for the sub.

Cut hole for the wiring terminal and silicone sealed all the joints.

Sanded all the rough edges

Used spray adhesive to stick on the carpet.

Carpet on the ends and cut the seams clean.

Cut out hole for the speaker and tested the fit (like a glove!)

The Install…....
As for the amp install, the first thing to note is that the wiring harness available from Technic (via this forum) is the key. It exposes all of the factory speaker wiring (except the center channel), a switched remote turn on lead as well as low-level (RCA) inputs from the factory head-unit. Technic also provides you with a fused 4 AWG power cable and ground cable with the appropriate battery and ring terminals. This harness is well worth the $90. It eliminates all the guesswork and is completely reversible with no side effects or cutting wires.

This harness also makes connecting the amp easy. You can do most of the wiring outside of the car.

Once wired up it should look something like this (depending on your amp and speaker configuration).

Now for the car, I started by removing the floor board and battery cover in the trunk.

I used a panel pry to pop up the middle of each plastic push pin holding down the trunk lining.

Used a Torx screw bit to remove the tie down anchors.

Removed trunk liner to expose the factory amp (driver side well)

I flipped up the plastic lever to unplug factory harness from factory amp.

I then connected the power wire to the positive(+) battery terminal (be sure to remove fuse first!). Then ran the power cable along the back trunk wall (below the latch). It tucks nicely underneath the plastic trunk liner trim piece.

I then connected the ground(-) wire to the existing ground terminal bolt on the driver side wheel well above factory amp. Once grounded, I re-connected the fuse on the power lead and used the factory amp mounting bracket (and Velcro) to secure the new amp in place.

I made sure to position the new amp directly under the removable plastic tray (driver side wheel well) so that I could make final tweaks without needing to remove the trunk liner again.

I then put everything back together, wired up the subwoofer and DONE! Now time for the tweaking…....

Tuning (aka tweaking)…....
Probably one of the most important parts of any stereo install is getting the relative levels and crossover points right. While there are general guidelines, and definite dos and don'ts, some of this is dependant on the type of music you listen to and your personal preferences. Tweaking involves two main things. Setting your crossover points and setting your gains.

Setting your crossover points:
The main objective here is to send the right frequencies to the right speakers. Being that I kept the factory speakers in place, I set my high pass filter pretty high because the stock door speakers are 4" drivers. A HP filter of 200hz sounded best for me.
The 'midbass' drivers took a little more fiddling, they can technically reproduce low (sub) range frequencies but I wanted to leave that up to the true sub in the trunk so I ended up settling on a band pass range of about (BP 80hz - 200hz).
The sub channel low pass was set to LP 80hz. I also used the 24db/octave setting to ensure a sharper cutoff of the higher frequencies to the sub woofer. Being that it's a 12inch true sub, I didn't want it trying to reproduce any of the mid bass. This configuration works well.

Setting your gains:
The goal here is to maximize volume while also minimizing distortion. There are various tools that help you with this (CD's, voltage monitors, etc), but without these, you can just let your ears be your guide. The first step is to set all your gains to zero, and focus on one pair of channels at a time. Turn the volume on your stereo up to about ¾ levels and slowly adjust the gain until you start to hear distortion. I like to dial it back a notch from there. This again is a matter of personal preference.
Your results may very but I found that the amp powered the inside speakers just fine with almost no gain.

Being that I was using channels 1&2 for all 4 door speakers, I decided to play around with numerous wiring configurations. I first tried to run the two pairs in parallel, but I found that the ohm load was too low and the gain had to be set to zero to prevent distortion at high volumes. I tried again with just the front speakers (no rear doors) but felt the car was not 'filling' with enough sound. I finally settled on a wiring the front and rear doors in a series configuration. This increased the ohm load on the amp (and thus reduced the power to each speaker), but I was able to get all 4 speakers to run clean at relatively high volumes. The amp has plenty of power to run all 4 doors in this configuration. I settled on a gain of just about ¼ turn.
For the midbass drivers I settled on a gain of about 1/3 turn. This allows the drivers to move plenty of air but not distort at high volumes.
Finally the sub, for this I settled on just under ½ gain. This was probably a bit more than I needed but I kept this configuration because I also added the HD-RCL remote level control so I can make real time adjustments to the sub bass from the front of the car. This allows me to change the relative sub bass level for different types of music.

Here are is a picture of the amp settings (just before I finished tuning the gains).

In the end I was very pleased with the result. I managed to get VERY good sound for under $700 and had minimal space loss in my trunk. Further, the entire system is reversible so I can put the factory system back together if I need to (if/when I sell the car). I hope this post will be helpful for all you DIY'ers. I'm always happy to answer any questions.

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      11-06-2013, 03:20 PM   #2
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Nice work!!
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