Build thread: Custom fitted 12" JL audio sub, with my own plans for C6

[bentwenty]

Evening all.
It's been a few months of owning my A6 3.0 TDI Quattro. Apart from a few minor things, it's been great!

But now it's time to get modding
First on the list is audio; for the most part I've found the Bose pretty good to listen to, not quite up there with the Focal and JL Audio setup I had my A3, but not worth the effort and expense of upgrading. Save for one aspect - the bottom end.
I find it to be very lacking in bass, so I have started to put in place a plan.

When I start a mod on my car, I like to plan and and execute it properly, and without compromising the functionality of the car too much. This is no exception.
I thought about building a sub into the spare wheel well, but I have a full size spare, and I used the spare in the A3 3 times, all of which got me out of a tight spot! So that's a no.

In the end I have decided to make it all from scratch with things I have already and some materials.
The box is my own custom design, once it's built and proven I will happy release the full drawings, but for the moment this is what it looks like

I have designed it to fit into the sloped section at the back of the boot, it's made from very solid 18mm MDF, and should be simple to build. I have made sure that it clears the boot floor opening, so you can lift the hatch without any issues, and it will pick up on two existing bolt holes under the carpet for mounting to save making a mess of the car. The driver sits up against the seat back (with enough clearance for the full excursion of the driver) so you can use the boot for your sh*te like I do without worrying about damaging the driver.
The box is also precisely the right tuned net volume for a JL audio 12W0V3-4. Note that this a sealed box (the hole in the side if for the speaker terminal box), it's not designed to go loud, although I expect it will. I am aiming for more very deep bass, I'm hoping to set the filters up to provide a natural musical extension to the bottom end of the Bose.

The driver is a JL audio 12W0V3-4, chosen as I have a lot of faith in JL audio, the don't over sell them selves, and make simple products that perform extremely well. This driver was in my price range and perfectly suited my required specs, it arrived this morning

The amp I have re used from the build I had in the A3, it's a JL audio JX250/1 amp, it's perfectly matched to the 12W0V3-4, and provides a very low distortion output at very respectable RMS power levels. It also has simple and very sensible controls and features.

To provide a bit more control, I have got an RBC1 from JL audio for remote volume control, I will most likely set it nicely into one of the dash blanks.

Power for the amp will come directly from with battery in the boot via a 50A fuse and 4AWG wire. From my previous reading, a switched live and pre out signal are both available at the big black connector on the Bose amp, so that should be no problem.
To connect it all I have a good selection of wire and terminals

I am currently at the stage of finalising the box plans before printing them off A3. At the moment it looks like a standard sheet of 606 x 1220 x 18mm MDF from B&Q will make the entire box.
I am also working out how to fit the JL audio amp into the Bose rack.
It's definitely possible, and once it's in there I'll pop a pair of PC fans and a digital temperature controller in there two to keep everything cool. This worked great in the A3 even in 40+ ambient in France with another JX360/4 4ch amp next to it!
To make it all fit, I'm planning to cut out the empty bottom shelf of the current Audi rack, and replace it with MDF to fit the JL audio amp.

I will update when I next do anything interesting, any questions - fire away.
Ben

 

[Jconway651]

NX9 do i spy? someone work in aerospace?

 

[bentwenty]

Right on the money, it is indeed NX9.0, and yep I'm an electronic/hydraulic engineer at an aerospace controls OEM.

Since the first post I've finished up the DWGs and printed them A3

I've been having trouble with the NX plotter, so it printed them out with parts hidden in certain views, hopefully I can for that before I release them.

I've also done a proper job of terminating the 4AWG live feed, fuse and earth strap with industrial motor crimps ready to install.

And I've bought the wood, I bought a full sheet of 18mm MDF from B&Q for £20, I will only need about half (the parts can be cut from a sheet that is 2200 x 430mm, thanks NX), but I will make use of the rest for bolting the amp to abs making the cooling system. B&Q cut it in half for free so it fit in the car, and I have nice square edges

 

[MarkWizard]

Watching this eagerly mate and agree re lack of bass. I have a nice JBL sub and Alpine amp collecting dust in the garage just waiting to be fitted to my A6

 

[bentwenty]

Damn! Back to the drawing board!
Cut out the sides just now, not so easy in my small 'workshop' (shed) with my limited woodworking tools.

But when I went to do a test, fit, I ran into a problem! The angle for the front of the sub does not match the angle for the back of the seats!

After re-measuring everything, I quickly spotted my error, in my rough notes, I said the angle should be 78 deg, this or correct.

But when I drew it up in cad, I reversed the digits and put 87 deg!

Unfortunately this small correction will mean re-designing all the components as it will change the volume of the box. The volume is very critical for the sound I'm trying to achieve as it is tuned to the driver.

Serves my right for doing all the drawings post midnight after work!

 

[bentwenty]

Right, drawings an plans corrected, time to go an make V1.1!

 

[bentwenty]

Nearly there! All parts cut and test fitted nicely just now

The plans seemed to be correct. Tomorrow is all about glueing and screwing.
The it's on to mounting the amp. I have an idea involving the extruded sections of 90deg aluminium profile, so I'll try that out and see if I can make it work.
All the terminations for the wiring have been made, I just need to fit it all

 

[MarkWizard]

I too have the Bose system. Cheeky request but can you post a picture / instructions of where you tapped into the car wiring to get the input for your new amp? Thanks

 

[bentwenty]

I too have the Bose system. Cheeky request but can you post a picture / instructions of where you tapped into the car wiring to get the input for your new amp? Thanks

Yes of course mate, planning to do that tonight. I will post pics and details for the whole circuit when it's done.

 

[bentwenty]

Mark, your comment reminded me to look up the pinout for the Bose amp.
It's not as I remember: from my cursory research, the amp receives line level signals via the MOST fiber connection, and sends the power level signals to each individual speaker. This is the diagram I've been working to http://www.audi-portal.com/en/diagnostic/ecu_12415.html#1
I was hoping to find a line level signal to break into, but it seem they only exist inside the amp, and I front fancy breaking into it.
Now, the JL Audio amp does have high level inputs, but I don't want to connect them in parallel to a speaker as the speaker then becomes a microphone for the amp, and will give all sorts of nasty feedback and distortion (have have seem them make a loud 'boing' when you slam the door, things like that).
so my current plan is to disconnect the rear parcel shelf speaker as I doubt it does much anyway, and feed that straight into the high level input to the amp. my only concern is that that channel might have a high pass filter on it. I will check if it is later by playing a set of test tones and checking the amplitude of each with a scope.

 

[B5NUT]

Your best option is to go for an aftermarket solution and completely replace the Bose AMP, here is one product http://www.mobridge.us/ but it is just under £500 available here http://www.caraudioexpress.co.uk/mobridge-m1000-m-da2-pre-amp-rca-outputs.html

 

[B5NUT]

However you may be lucky tapping into the parcel shelf speaker. As you have the old Bose AMP, which was only in production for around 10 months then that parcel shelf speaker is classed as a sub, from mid 2005 all Bose equipped cars came with the Bose 6000 AMP where the parcel shelf sub was done away with and two surround speakers were put in place.

 

[bentwenty]

Yes I agree, that would be my best option. However I don't have that kind of money to spend, I have out this project together mostly from leftover parts...
I had a quick look with a scope earlier (battery powered so I didn't load the amp down to ground), it looks like with the speaker in circuit, there is a fairly severe EQ applied with a peak at about 300Hz. Not very good! I will do some more poking later a plot the frequency response of it to see if it's any good. I know that Bose like to EQ everything, that's how they make their systems sound 'good'...
As for classifying the parcel shelf speaker as a sub, well it's about 4" diameter and very light weight, so it's not going to produce much bass... I'm sure your right about the layout though as I can only see one in the parcel shelf and mines late 2004 on a 54.

 

[MarkWizard]

Thanks Ben & B5NUT!

Mine is a 2007 57 plate Avant so don't have a rear shelf speaker. My Alpine amp also has a speaker / high level input but in light of everything will probably just leave the audio standard. Anyone want to buy an Alpine amp?

 

[B5NUT]

As you have the Avant & the later Bose6000 AMP, you will have the small surround speakers in the D pillars, think if you tried to tap into one of them it's not going to sound right.

 

[bentwenty]

More progress:
Those parcel shelf speakers are no good. They are actually 2x 2ohm speakers connected to a single amp channel in series, making 4ohms. Once they had been disconnected, this was the frequency response for their amp channel

as you can see, there is a very severe EQ applied, peaking at 450Hz and rolling off steeply either side (looks like -12dB per octave). This is no good at all for a sub! This is fairly typical of a Bose system, medium quality components made to sound 'good' with very steep EQs.
That leave three options for me:
1) break into the Bose amp and pick up the output from the digital to analogue converter from the optical input, I will have it int bits tonight to investigate.
2) use one of the front or rear bass speaker outputs with the speaker still in circuit. I don't like this option as discussed before.
3) disconnect both the rear bass speakers and use their outputs, perhaps I won't miss them with a 12" sub in the boot lol.
On a positive note, the sub box is looking good, is screwed together now, going to glue tonight if I get a chance.

 

[bentwenty]

The main Bose amp was a bit of dead end, all of the signal processing is digital (two different CPUs and A PIC16F series), there are some analogue power amps, but I suspect they are all post EQ as the go directly to the output pins

However, this auxiliary amp looks promising, it's a class D 100W FET amp, most likely mono. What does it power?
The Bose number is 416007, it's connected to an Audi loom that gives it the Audi part number 4f0 035 223 b. It sits under the bottom of the amp rack in the boot, but what does it run?

 

[B5NUT]

4F0035223B is classed as a Base amplifier, after a quick google I found quotes like "100W, 12VDC, analog input switching amplifier".!

 

[bentwenty]

Yep that's why I found, I have a rough pinout for it now, but I'm not sure what speaker it drives.
Unfortunately as I was poking about on it earlier with my scope, I think I managed to short one of the rails to ground, there was a few clicks, and now the whole mmi system won't boot lol
I have found a 30A fuse that's blown, so with any luck replacing that will fix my balls up lol.
As it seems to be mono, I wonder if it powers the centre speaker in the dash?

 

[bentwenty]

Yep that's why I found, I have a rough pinout for it now, but I'm not sure what speaker it drives.
Unfortunately as I was poking about on it earlier with my scope, I think I managed to short one of the rails to ground, there was a few clicks, and now the whole mmi system won't boot lol
I have found a 30A fuse that's blown, so with any luck replacing that will fix my balls up lol.
As it seems to be mono, I wonder if it powers the centre speaker in the dash?

 

[B5NUT]

The centre speaker in the front dashboard is small, only 2" at most. My guess is to help power the left, right & rear base speakers.

 

[bentwenty]

Possibly, I know what your saying about that speaker, it does sound very small and tinny when it's switched in for a phone call.
The amp has one Bose 416007 chip, which seems to be a single Chanel FET driver, and 4x N channel FETs, consistent with a fairly beefy class D amp.
The driving of the main speakers including the bass ones seems to be done by the main Bose amp, the connections ring out to the amps inside that.
I think I need to get my copy of Elsawin back up and running lol.
Good news is that fuse has sorted the rest, so I'm back to where I was...

 

[bentwenty]

More progress: I spent this evening filling and sanding the the box before paint. I used plain old 2 pak filler, worked a treat!

It's now all sanded back and ready for a couple of coats of gloss black when I get the chance.
In other news, after some farting about with VCDS, I have found that the extra Bose amp I bumped into seemingly doesn't power anything! Unplugging it throws no error codes, has no effect on the sound of the car, and it still plays all the test tones from VCDS! I can only assume it's to power the spare wheel well sub. And is either fitted to all, or mine had the sub, and it was removed and coded out at some point.
Either way, I will poke about on the connector, and hopefully find line level audio with a sensible EQ (or no EQ if I'm really lucky) on it.

 

[KristoffV6]

This is interesting stuff, I'm building a twin 12" sub box for my A6 and I've as yet no idea where I'm going to get the signal for the amp from. Stupid MMI system.

 

[bentwenty]

Before you get too far into your build, do some more research into a signal source. I certainly wish I had!
It may be easier if you don't have Bose, but if you have Bose, it's definitely very challenging to do.
Since my last update, I've got it fitted and sort of working.
The hardware is all quite straight forward, I cut the bottom off the Bose rack, and made a piece of MDF with the right profile to fit on the chassis. I then made an aluminium support for the Bose rack and the MDF

Power wiring was easy, I used an existing earth point, and a spare bolt on the 12v bus on the boot fuse box

I wasn't able to find any switched lives on the Bose rack, they all seem to have a permanent live, and be switched by a CAN signal, so I ran a switched live from the passenger side fusebox.
The sub is temporarily fitted, I tried to paint it last weekend, which didn't go well at all as the MDF absorbed a lot of the paint, so I'm going to carpet it with black carpet this week

Now the signal - it's not good news! I was able to find line level audio at the input to that in used extra amp

But it's got a very nasty filter on it, this was plotted with my Philips CRO and excel

ouch!
That was plotted with the MMI EQ flat! It's obviously been designed for a cheap and nasty Bose sub, so all that sub 40Hz goodness is missing! Very annoying as I have tuned my box for 28Hz, which is the Fs of the JL audio 12!
Almost as annoying is the peak and then fall off towards 100hz, again territory which my sub would be right at home in!
For the moment I've connected to that as I don't have anything else, and at least it's line level. But it sounds crap! Lovely on the odd note, very loud and deep, but a lot of notes are simply missing! And it gets very muddy up towards 100hz.
Now, I have a couple of possible solutions up my sleeves.
I've had another good look around the Bose amp, as far as I can tell, all the signal processing is done digitally, no surprise there. So unless I can program one of the devices, that's a dead end. Programming them may not be completely out of the question though, I've made a complete parts list of the DSP side of things, there is a Pic16Fxxx and and atmel device, both of which I can program. So I may look into that a bit deeper.
I will also plot the FR for all of the outputs, I'm thinking of buffering a couple of the best looking channels into high impedance op amps, applying my own filters, then feeding them into a summing op amp to give an aggregate signal which may be useable.
The easiest option would be to create a notch filter with some gain for the signal I already have, I may be able to recover some frequencies. Although this is a little limited as I can't amplify what simply isn't there, and I risk a lot of noise as well.
Another possibility is the third connector on the Bose amp, anyone know what it does? I think it's a 12pin connector, next to the optical connector. Although I'm not holding out much hope!
Lastly there is the proper solution, something like this http://www.caraudioexpress.co.uk/mobridge-m1000-m-da2-pre-amp-rca-outputs.html
It a little out of my price range, and a bit overkill for my purposes as I don't intend to replace all the speakers (as much as I'd like to!) as it would be far to costly. But it is the proper way of doing things!
I would be very interested to hear anyone else's thoughts!
Ben

 

[KristoffV6]

Looks like an absolute nightmare to be honest.

I am determined to get some decent bass in the A6 though, everything else on the car is done now. If I have to use a £600 MOST fibre optic preamp and replace all the speakers and amps in the car, so be it. I don't have bose so I wonder if I'll have any better luck? I doubt it.

 

[bentwenty]

Evening all, apologies for the lack of updates! I've been very busy with work and another very exciting Audi related project! More to come soon.
Anyway, since last time I've carpeted it with the help of my lovely girlfriend.
It's come out really well! The white stuff on the corners is excess spray adhesive and will get scraped off at some point.

I have also now got a bit more of a feel for the sound. It's very nice and deep, but the missing parts of the frequency range are very noticeable and irritating!
I have looked in more depth into reverse engineering the MOST25 protocol, so far I've not found any useable information on it.
So I will be designing a set of filters and op amps to attempt to correct horrible Bose EQ. It won't be ideal, but it should help a lot!
Also now that I'm happy with the box design, I'm very happy to upload the drawings for anyone who may be interested.
Ben

 

[KristoffV6]

I'm having a total nightmare with this, I can't believe that its so hard to get a full range feed. I've a box built with a pair of 12's firing through the ski hatch, but I can'get get even a half decent signal to feed it with. In theory it should be possible to eq the signal to get it a bit more even, but that will need loads of eq as in some places its almost 50db down! But what I also suspect is happening is that the eq changes depending on the volume level, so you'd need a dynamic eq which is getting into the realm of impossible.

I might just buy the MOST interface and replace the entire system in the whole car with standard two way actives in each door and a 4 way amp. It's looking easier than trying to get a decent signal out of the factory system.

 

[JUICE A6]

Hey a world I saw at 3 at about 3 months ago where you can change the base on the MMI from leather interior to cloth interior

 

[JUICE A6]

I've been trying to keep notes on the different websites because when you try looking back up you can't find them again ain't that a kick in the ***

 

[bentwenty]

I'm having a total nightmare with this, I can't believe that its so hard to get a full range feed. I've a box built with a pair of 12's firing through the ski hatch, but I can'get get even a half decent signal to feed it with. In theory it should be possible to eq the signal to get it a bit more even, but that will need loads of eq as in some places its almost 50db down! But what I also suspect is happening is that the eq changes depending on the volume level, so you'd need a dynamic eq which is getting into the realm of impossible.

I might just buy the MOST interface and replace the entire system in the whole car with standard two way actives in each door and a 4 way amp. It's looking easier than trying to get a decent signal out of the factory system.

Yeah that's the conclusion I am coming to. I think you may well be right about the DSP being active as well, although I've not investigated that.
I had a think about making an inverse filter, and have pretty much decided it's not possible. As you say, it's up to 50dB down in places, so would need some very high gain (noisy) amps on the output. Also having multiple analogue filters often leads to an oscillator if not very carefully designed!
I have been talking to someone I know who works for Executive car audio who has just done a build in a C6 using and Audison Bit One DSP. They seems to offer a few different DSPs with optical support, although they don't specifically say MOST support. Worth checking out. http://www.audison.eu/index.php?page=productLine&id=15

 

[Markjb]

A great follow - hope you get the lower frequencies sorted