[Prof. Oak]

I had received my m40 with the HK system and thought it would be enough, but it was apparent right away id have to do something. I dont need ground shaking bass but i am used to a bit more based on what i listen to (EDM/House and Rock/Alt). I tried the Bavsound under seat woofers upgrade, and while an improvement, still not what i was looking for. I noticed in alot of my music notes seemed to be missed and i realized the under seat "woofers" are more mid-range drivers. So i looked to do my own DIY and finally have what im looking for. Might not be the cleanest install but it works and its secure, and its out of the way. Best part is no rattles or annoying vibrations either.

A simple, quick write up below. Word of warning, this is very easy to do, however install at your own risk, i am not responsible for any injury or damage you may cause by doing this yourself.

Parts:

Everything bought from crutchfield, however you can shop around elsewhere if desired.

JL audio powered sub/amp combo--JL Audio ACS110LG-TW1

Power/ground wiring kit--Crutchfield CK8

RCA patch cables--Crutchfield 2-Channel RCA Patch Cables (6-foot)

Remote bass knob(optional but helpful)--JL Audio RBC-1

Technic PNP add a sub harness (very important)--HK(688) Booster harness with LOC150i---link below

https://technicpnp.com/product/hk-op...oster-systems/


And that's it, the install is fairly straight forward, the biggest thing to pay attention to is what kind of factory system you have and order the correct harness from technic PNP. You can email them if unsure they are very helpful. I had the factory Harmon Kardon which is option 688 on your build sheet, this is important because the HK system uses a RAM and puts out too much voltage for the add a sub option, hence why technic offers an included LOC that mates directly to their harness, no fuss and extremely easy. You can of course choose your own LOC but honestly i wouldn't, just use the Technic one.

Remove trunk side panels to access the factory RAM module in the right hand side, and unscrew and remove your trunk lid that lifts up.
You can remove the carpet "bin" as well underneath this just lifts right up once you've removed the trunk lid. I layered 1/8th thick dynaliner down here to reduce vibration and the result has been great. You can then reinstall the carpet lining and proceed with the install.

Remove the metal bracket holding in the factory RAM, its 4 10mm bolts.

Unplug the factory harness and plug in the one provided by technic, then install the factory harness plug now to the plug left on the technic harness for it, then mate together the remaining connectors on the harness (green and white connector to green white connector, etc) and it leaves one connection left, which goes to your LOC. (LOC is the black box with the "wavetech" logo on it in the photo.)

You can then reinstall the metal bracket, zip tie things as you want. With the bracket reinstalled, i mounted the LOC (small black box) to the front side and then plugged in the connections as shown.

The LOC has your remote turn on wire and the two RCA cables which plug into the powered sub, i ran all this under the rails on the floor for the sliding cargo rings and into a small hole i created in the bottom of the carpet liner bin the sub sits in, nothing can be seen from the top once the trunk lid is reinstalled.

With this all wired all that's left is power and ground, i routed the ground cable from the powered sub back under where the LOC is and to one of those metal bolts holding the bracket in, scrape off the coating on the washer to ensure a solid electrical connection. In the provided photo you can see the ground cable, its the bottom right bolt and the black wire coming off of it is the ground.

For power, i routed to the battery power connections directly to the right of the battery, there is a large red plastic covering protecting two cables, gently lift up the covering and access the 13mm bolt holding one of the two cables on, i chose the right most of the two. This is the only place you should be grabbing power from, not from the rectangular red section all the way to the right with multiple terminals, this will cause some irregular settings in the car to change for whatever reason. Get in and out of this area and do what you need to do, you don't really want to mess with the stuff here for too long.

Place your fuse and route the power cable to the powered sub and this should be it. I routed my bass knob to the same place as the LOC for ease of access. Good luck and if there are any questions ask here i will answer what i can, i didn't take a lot of photos during the process as i didn't really anticipate writing this but i see a lot of "need more bass" threads and figured id throw this out there. Good Luck.

Oh BTW that wooden bracket is only there to stop the JL sub box from moving around while i drive, i measured it and cut exactly to fit and does a dam good job, was meant to be temporary but honestly i might just leave it.


******update 1 year later MAR 2024, i still have left the wooden bracket there. Literally no movement of the setup even during aggressive driving over the past year and everything still works perfectly fine as if factory. Ive had zero issues with sound, etc. Ive done some minor in cabin tuning adjustments using the EQ in idrive 7. I meant to get it tuned since i dont really know what to do with the gain/eq, etc settings on the AMP itself but i think ive gotten used to the sound by now, im no sound professional. There is still zero rattles, i did install a rubber license plate gasket in between the holder and the plate as that was really the only place you could get it from.



After some questions ive attached a third image with some things circled with matching numbers to the descriptions below to make it easier to understand.

1. The RAM module is on the back side of this metal plate, this is where the connections from the pnp harness will mostly be hooking up. In the photo you can see the green and white wires that i mentioned above.
2. This is the LOC, which i mounted to the front side, it made the most sense and i was able to zip tie it in.
3. This points to the blue remote turn on wire that will run from the LOC, under the trunk rails, and eventually to your AMP.
4. This is my grounding point for the AMP, remember to sand both sides of the contact points to ensure a solid connection.
5. This is where all cables running to the AMP/SUB in the trunk space were routed under the trunk floor rails, and into the under trunk compartment.

[devil84]

Thank you for this write up. Really useful.

Regarding the LOC, does this need a separate power and ground cable?
Where does this draw power from? The website suggests plug and play?

[ASAP]

Really nice write up... but what does it sound like?

[NYRangers79]

You gonna sell your bavsound subs?

[HuskerNSC]

Interested in how it sounds as well, given it is buried in the storage tray.

[Da X3]

Any sound clips please. Interested.
Thank you

[Prof. Oak]

Apologies, been on deployment and havent checked here much, to answer some questions:

The LOC did not need an independent power source, it does have the RCA connections and remote turn on wire that goes to the amp, but it gets power and other inputs from the harness provided by technic.

No i am not going to sell the Bavsound underseats, despite being not what i wanted they are an improvment over stock for a mid range driver

I wouldnt say its "buried" in the storage tray, we're talking about a simple thin lid that closes over it, most sedans have more in the way for their trunk installs and nothing is hindered. Ive installed subs into a variety of different makes and models in different styles and to my ears there is no sound loss or anything from its location.

Sound clips i have none on me, i am still overseas at this point. However, i can describe to you it solved all the issues i had with the factory audio not having enough low end, and didnt end up being a rattle trap either.

[AlterZgo]

Prof. Oak Thanks for this write up. Very helpful! If I were to get a Bimmertech amp upgrade that is basically a pllug and play replacement for the stock HK amp, do you think I would still be able to add a subwoofer using the same equipment and process that you did?

[avi66]

Originally Posted by AlterZgo

Prof. Oak Thanks for this write up. Very helpful! If I were to get a Bimmertech amp upgrade that is basically a pllug and play replacement for the stock HK amp, do you think I would still be able to add a subwoofer using the same equipment and process that you did?

What version of iDrive is your car ?

[AlterZgo]

Originally Posted by avi66

What version of iDrive is your car ?

I have the version right before they ditched all the physical buttons and controls so I think that's version 7? Is there way I can check definitively? It's a 2023 X3 M40i.

[avi66]

Originally Posted by AlterZgo

I have the version right before they ditched all the physical buttons and controls so I think that's version 7? Is there way I can check definitively? It's a 2023 X3 M40i.

2023 G01 = iDrive 7 and RAM audio architecture.

Originally Posted by AlterZgo

If I were to get a Bimmertech amp upgrade that is basically a pllug and play replacement for the stock HK amp

You may be aware, but you can’t “replace” the stock amp in a RAM architecture BMW. This is because the amp is an integrated function of the RAM along with other things like ASD, radio receivers, DSP, DAC etc. The head unit in the X3 (MGU18) is connected to the RAM digitally via what BMW labels as Ethernet, and the RAM connects digitally to the HK booster according to BMW.

Again, you may be aware that the Bimmertech offering just hijacks the heavily processed and already amplified analogue speaker outputs from the RAM. Hence, the stock BMW amp and other audio processing isn’t replaced or even bypassed.

Attaching a powered subwoofer could follow similar lines i.e hijacking the appropriate amplified speaker level output which could work with pretty much any amp.

[AlterZgo]

Prof. Oak avi66 and anybody else who has some ideas...

I bought the Technic harness and tried installing it in my 2023 X3 M40i w/ HK 688 audio (RAM) along with a Rockford Fosgate Prime mono subwoofer amp and a JL Audio 10W6V3 subwoofer in a ported enclosure and I’m having some issues. Specifically when everything is installed, I lose the right rear audio channel. Is this normal? Is the signal for the Technic harness basically pulling from the right rear speaker channel thereby taking away that channel?

Also, there is something wrong with the signal as the subwoofer will distort and rumble at certain frequencies and it does not sound clean and solid. I checked my installation and noticed that when the harness is engaged, some of the pins are pushed out a bit on the back of the harness (see picture attached) so i pushed the pins back in place but I’m still having the same issues. The amplifier is not going into protect mode or shorting out and I have made sure all of the wiring is clean and correct. All of the equipment I’m installing is brand new.

Here’s all the details of my car and equipment:

• 2023 BMW G01 X3 M40i w/ HK 688 audio
• Technic Top Hifi (option 688) RAM + Booster Add-an-Amp harness kit
• Rockford Fosgate R2-500x1 Prime mono amp
• JL Audio 10W6v3-D4 (dual voice coil 4 ohm sub wired in parallel for 2 ohm load in ported enclosure)
• 4 gauge wiring kit

I am getting a signal and sound from the subwoofer but it doesn’t sound right. It almost sounds out of phase and doesn’t get very loud. Also, as indicated above, with the harness hooked up and even with the subwoofer disconnected, there is no audio coming out of the right rear channel. I’ve rechecked the wiring multiple times and reconnected everything multiple times including moving the ground to different parts of the car and directly grounding to the chassis. I’m sure the wiring is correct as I’ve installed many full blown car stereo systems before so I do have some experience in DIYing car audio.

I understand it’s hard to diagnose this as it could be for a variety of reasons but would appreciate any insight.

Here’s a picture showing the pin being pushed out a bit when harness is connected. There were more that were pushed out so I pushed the pins back in with a small pick to make sure the connections were solid. The amp is turning out and there is sound coming out of the subwoofer but something is not quite right and I would appreciate any help or ideas on how to sort this out. Thanks!

[Must_Go_FASTER]

Don't think those pins are supposed to be doing that, but also can't tell ya if that's causing your problems.

Contact Technic and let them know what's going on. They'll likely be able to diagnose the problem and I'd guess they'd replace the harness is it's part of the problem.

It's been a couple years, but their customer service was excellent when I had questions about their harness and how it would all work.

[avi66]

Originally Posted by AlterZgo

Prof. Oak avi66 I’m having some issues. Specifically when everything is installed, I lose the right rear audio channel. Is this normal? Is the signal for the Technic harness basically pulling from the right rear speaker channel thereby taking away that channel?

Just a guess, but the loss of the right rear channel may be a bad connection if the third party harness fits between the BMW connection and the RAM.

I’d imagine the feed for bass level output would come from the HK booster, otherwise why connect to it.

[AlterZgo]

Originally Posted by avi66

Just a guess, but the loss of the right rear channel may be a bad connection if the third party harness fits between the BMW connection and the RAM.

I’d imagine the feed for bass level output would come from the HK booster, otherwise why connect to it.

Thanks. Another member pointed out that I was likely connecting the harness to the RAM module rather than the booster and he was right. I re-read Prof Oak's instructions and realized the module in front is the RAM module and I have to access the booster by removing the 4 screws holding the black plate the RAM module is attached to and the booster is behind that black plate.

[AlterZgo]

83883 Thanks again for your help in figuring out my issue. Everything is installed and working properly now.

For anybody reading this in the future, Prof. Oak's instructions are spot-on. The Technic harness connects to the booster, not the RAM module in front. The booster is attached to the back of the black metal plate that the RAM module sits on. Unbolt the four screws and just pull the black bracket towards you and you will see the booster bolted to the back of that black metal plate.

In this picture I have circled the four bolts that need to be removed. The red X is the harness connecting to the RAM module. Leave that intact. I initially connected the Technic harness to the RAM module and it didn't work right.

The red oval is where the harness to the booster is located. Once you unbolt the 4 screws, peel that black mounting plate back and you can access the harness connected to the booster. Install the Technic harness into the booster. You can tell it's the booster by the diagonal heat sinks on it.

[83883]

Originally Posted by AlterZgo

....Everything is installed and working properly now....

Woohooo! Glad you got it all working. Great additional documentation.

[jocamryn]

All those wires and harnesses....that looks super intimidating

Originally Posted by AlterZgo

83883 Thanks again for your help in figuring out my issue. Everything is installed and working properly now.

For anybody reading this in the future, Prof. Oak's instructions are spot-on. The Technic harness connects to the booster, not the RAM module in front. The booster is attached to the back of the black metal plate that the RAM module sits on. Unbolt the four screws and just pull the black bracket towards you and you will see the booster bolted to the back of that black metal plate.

In this picture I have circled the four bolts that need to be removed. The red X is the harness connecting to the RAM module. Leave that intact. I initially connected the Technic harness to the RAM module and it didn't work right.

The red oval is where the harness to the booster is located. Once you unbolt the 4 screws, peel that black mounting plate back and you can access the harness connected to the booster. Install the Technic harness into the booster. You can tell it's the booster by the diagonal heat sinks on it.

[spangle1980]

Originally Posted by jocamryn

All those wires and harnesses....that looks super intimidating

Thus this forum :-). Like minded people to help in a challenging sitch.

Like me, there is no way I would have ventured to retro-fit the (chip shortage initiated) rear lid kick closer without massive boost of love from this forum.

GO YA'LL, and a very Merry Christmas to one and all.

[RickBasso]

If anyone is interested, I have just installed a Rockford Fosgate amp and RF 10" shallow depth sub in a custom made (by me) enclosure in the small compartment underneath the rear floor panel thingy. I could not get Technic to ship to Australia so I had to make an educated guess as to which wires to tap into coming out of the Bass booster. In the end it was pretty obvious TBH...I used an amp with a high input (speaker wire) capability and auto turn on so no need for a LOC nor an accessory remote feed. Works well and fills the hole that the HK system had in the bottom end dept. Very easy spot to do the install as everything is close, ie, bass booster, battery, ground, and minimal unreversable damage.

[avi66]

In case it can help anyone, here are the pinouts for an ALEV3 HK Booster DAC & AMP module used in LCI G01.

TYPE Key - A = Ouput and E = Input

[spangle1980]

Originally Posted by RickBasso

If anyone is interested, I have just installed a Rockford Fosgate amp and RF 10" shallow depth sub in a custom made (by me) enclosure in the small compartment underneath the rear floor panel thingy. I could not get Technic to ship to Australia so I had to make an educated guess as to which wires to tap into coming out of the Bass booster. In the end it was pretty obvious TBH...I used an amp with a high input (speaker wire) capability and auto turn on so no need for a LOC nor an accessory remote feed. Works well and fills the hole that the HK system had in the bottom end dept. Very easy spot to do the install as everything is close, ie, bass booster, battery, ground, and minimal unreversable damage.

Did you feed both left and right low frequency output to the one sub input? Just curious about this for future expansion. Pics would be good of your rig in the boot if possible. Does it provide the low frequency thump that one deserves sir?