Whiterabbit's 2015 Mercedes GLA 45 AMG

[Whiterabbit]

I was hoping to go to a local show and surprise the guys with a new car and install, but with shelter in place, that's not happening any time this year. So I may as well post up my car. It's incredibly plain, but maybe one or two of the small tricks can help to inspire others for some aspect of their car.

Anyway, on with the car! It's the first performance car I've owned, and it's pretty doggone fast!



Just a rinky-dink 4 cylinder engine, but it makes some good power. The real eye opener was that it comes with a bunch of Benz tech that I had no idea I needed. It sticks to the road like glue, and even more now that I have Potenza RE-71R's on it. differential AWD with torque steer, a Dual-Clutch transmission that shifts ridiculously fast. The turbo lag is extreme, but still theoretically gets me from 0-60 in near 4 seconds. Which means though the 0-30 time is awful, the acceleration from 30-110 is warp-ridiculous to compensate. It's a hoot to drive! And the hatch means I can still move some small cargo, fit my kids in the back comfortably, etc.

After I put a piggyback computer on it, I was able to find a local tuner shop with a 4-wheel dyno willing to help me out



The internet consensus is that the AWD/rear differential sap 18% of the crank HP. Assuming that is true, I'm putting about 420 HP down at the crank. I like the thought of being in the 400 club...



Regardless of the power level, it's fun to drive! I drove from San Jose to San Diego two years ago and took 14 hours to do it, by taking only super-windy backroads until I hit PCH above Malibu. I was totally tense and tired when I arrived at my destination, but it was an absolute joy.



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Anyways, on to audio, the interesting part!

The install is uber-simple, and no-fluff, so you guys might find it a bit boring in design. Hopefully there's something of interest in the execution to make it neat and fun:


Source:

OEM. Besides being easy, and good enough, it also has a USB input, an ipod input, and an SD card input. So, I put all my WAV on a giant ipod, all my MP3 on an SD, and my wife's entire music collection on a USB stick. Now I have ALL my music in my car at the push of a button, and all my wife's music too! And bluetooth is still there for Pandora. So my bases are covered!


Signal processing:

Factory - I use it as a MOST adapter. That's cheaper than buying one
JBL MS8 - deconstructs the 8 outputs of the factory amp, cleans me up, gives me 7.1 upsampling (I'm using 5.1), and gives me a basic tune.
miniDSP HD - I am using two of these. 4 inputs, and 8 outputs. They post-process my mains, center, and sub. HD because apparently these two letters make it better, and they are cheap enough. This gives me all the processing power I could want. The rears stay processed only by MS8. It's enough.


Amps:

JL HD 600.4 and 900.5. 9 channels total cover the entire car. I have come to really like the JL technology in the HD amps, and the form factor is hard to beat. Also, I like the input terminals and locations on the amp. All in all, it's a great sounding amp with good packaging.


Speakers:

Center: Scanspeak Illuminator tweeter, Focal Be3 midrange, and tangband midbass of some flavor.
Mains: Morel Elate Ti 6.2 component set
Rear Midbass: Rainbow Reference (patched in as Mains via separate channels of the miniDSP to experiment with midbass support. Fun reading: https://www.diymobileaudio.com/threa...visited.74088/)
Surrounds in C-pillars: Fountek FR88EX 3's
Subwoofer: Phase Linear Aliante 15SI 15" flat subwoofer. I'm going to be buried with this darn subwoofer.

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Some notes of undocumented stuff:

Standard power wiring. There's an access panel in the trunk that I mounted the D-block in, no fluff.

The OEM wiring was large gauge, so I used it. I cut the factory speaker output wires behind the trunk carpet. 8 speakers, 16 wires. I then crimped on molex pins and 2 pole/4 pole headers so I can reconnect them. That maintains the factory stereo 100%. But now, I unplug them and plug in my own molex pigtails. the amp outputs go to the MS8 inputs, and the JL HD amp outputs are routed to the molex tied to the car wiring. 100% clean and the stereo takes 15 minutes to electrical de-integrate it, and restore the factory condition.

SUPER simple.

On with the build!

[Whiterabbit]

Amprack

Trunk looks like this under the floor:



Not my car, but it's the same. No spare! Ouch! Just a bottle of goop and a 12 volt compressor. Well, no use crying about it now. OK, so, how to use the space? First, move the goop and compressor out. That gets stored elsewhere. The rest is reintegrated since it's the stereo stuff anyways. Factory amp, and factory sub. OK! trunk gutted, easy enough. Let's start with the amp rack.

I have feeble welding skills, but it's enough to get a job done. Maybe one day I will be a farm quality welder! Here is the base:



It gets a cross beam, sheet aluminum is screwed to that to serve as amp platforms, and that leaves just enough space under the rack for a project box to hold the miniDSP. Onward!



Now fit into the car. The whole thing is cantilevered from the seat mount bar, and floats. It's super-tight packed, and is the max for space efficiency possible. I need the space, I'm putting a 15" under here!




OK, so for some reason I have lots of pics of the miniDSP HD case, so here we go with that. I bought the raw PCB's because again, cheaper. I like cheap So, need to plan for the board height, and punch the face for the interface.


Power molex. I love molex plugs. Cheap, secure, easy to crimp, and available in the right sizes needed.



2x USB for control, DB25 for signal in and out (4 in, 8 out, = 12 RCA = 24 wires), and the 4 pin Molex for power.




USB bulkheads wouldn't fit with converter cables, so I needed to cut the cables and solder directly to the terminals of the miniDSP. no problem:



OK, button everything up, it's GTG




Location us under the center amp. It sits on three standoffs. So, screw the standoffs to the chassis, insert under the amp rack. Put the amp plate in place. Screw the miniDSP chassis to the amp plate. Screw the amp plate to the amp rack. Screw the amp to the amp plate. Done. Serviceability is "OK". good enough, takes 30 minutes to pull apart. But no need to service, the whole thing was built to be reliable.

Note the rubber bumpers between the rack and amp plate. Non-welded, it's important to make sure stuff doesn't rattle. And no-welding ensures I can use a different plate in the very off chance I change amps. These things are cut 1/4" undersized so everything looks like it is floating. No universal compatibility, here.




And, done!

[Whiterabbit]

Speakers

This is the boring post. Everything is very plain.

Sadly, I guess I didn't take any pictures of the work on the center speaker. Oops! Well, it's straightforward. Car trim came out, traced onto hardboard. Cut the hardboard with a jigsaw, and same it until it is PERFECT. Then use that as my template.

Speaker is recessed, the tweeter was installed off center.

I made a passive network for the tweeter, 12 db/oct. the Focal Be3 rolls off naturally. Overall it makes everything sound very natural.




No, you didn't see this. Move on.



Stock doors. Painful! They are not screwed together. They are riveted! I had to drill out 40 rivets to get the panel off. The SPEAK is rived in place with plastic rivets! I had to drill out three plastic rivets to remove the speakers! That's just crazy. Oh, and the big rivets at $1.50 each at the dealer, so that's $60 in RIVETS just to replace some speakers. Holy cow.

Obviously, the design makes it so that in the future, the 6" speaker comes out and ALL access is now done through the speaker hole. No more rivet replacing!

You wouldn't believe how ridiculous it is to clean up a drilled out rivet.



Clean inside the door, but we can do better. Couple SDS tiles, butyl rope, and button back up.



KISS rules for speaker rings. I use MDF because it is dense, dimensionally stable, and reasonably waterproof. They hold screws, both wood and machine. They are stuff, which you cannot say about the plastic material!

For extra waterproofness, I spray with filler primer then coat with my favorite automotive/not automotive paint. Chalkboard paint. This stuff rocks, it makes wood look like ABS plastic. Good enough for most automotive behind-the-scenes aesthetics!




And there you have it. Rainbow reference in the rear doors, and Morel Elate Ti in the front doors. No muss, no fuss.




Next, the tweeters. These are also super simple. Pop out the sails, cut as little as possible, high-temp hot glue in place, make sure they are fully supported, add my favorite molex terminals, and re-install.









Blasphemous, but I used the passives for the front. KISS, this car, and I have tons of processing power on tap to get as close as I can to nirvana without separate control for the tweeters. I can manage. These guys get tucked up above the kickpanels, out of sight, out of mind.

[Whiterabbit]

Rears

For some reason, I took lots of pictures of these. Probably because of the machining involved with the mount. But other than that, this is the least fussy part of the install.

Rears are held in with rubber friction cups, and I elected to maintain that mounting system for these drivers. That meant the material had to be stronger when thin than MDF, so I used a hardwood. It all looks the same when covered with filler-primer and chalkboard paint anyways. I'll let the pictures tell the (simple) story.

[Whiterabbit]

Sub box

Let's see if I can coax this into some semblance of sense. it's simple in concept, but there's lots of test fitting needed. The goal is simple: Look like the OEM box. Sort of. But that's what the inspiration is. Some bland old ABS box that has a speaker in it. That's it. THAT is true "stealth" if it could be called that. Anyways, here we go!

The walls are 2 inch thick MDF:



Following the same OEM design, with a shelf for the OEM amp, neck down the top, just big enough for a 15" subwoofer.





Minimum clearance on all sides, but still, I MUST have clearance, or else it will look like it's "flowing" into the car, which is not the OEM look we are after! We want something that looks like a roto-moulded box that is bolted in place.



Prepping the glass.







This stuff is cool. It's like an open cell foam designed for glassing. Like an i-beam, it adds thickness without bulk, raising stiffness to a huge degree without adding weight.



I like this stuff. It is not glass matting, so it conforms to 3D surfaces, But it is SOOOO thick. it drinks resin and bulks up huge. At the same time, it is matted enough to ensure zero pinholes. Sweet.



Make sure the box clears. 1/8"? yep, that clears!



whew! That dog will hunt!



Looks pretty? I used some standard fiberglass weave. No matting, no fancy whatever. The FIRST layer is a standard 4/6/8 oz weave. It is the best material for conforming to 3D surfaces, and leaves a finish so clean, it's used to make fancy wooden canoes and kayaks. On top of that, the bulk 14Oz glass cloth. On top of that, that foam sheeting. On that, more 14Oz cloth. On that, a final layer of standard weave. Makes it look pretty!

On top of that go the rings of course. Glassed right in.



Now build up the rest of the layers



Test fit. The subwoofer is surface mounted on one board



Second board is cut over the OD of the subwoofer so it looks flush mounted. Then put the waffle grille over the subwoofer for protection. Then, cut another layer of 3/4" MDF to sit over that. The backside of the top MDF gets rabbeted out so that the rabbet acts as a clamp, and clamps the grille onto the subwoofer. It's also cut to be a tight fit to the grille so it doesn't slide around.



Maybe it's 1/2". Can't remember



Now we start adding the body filler. This will be painted, so can't have so much as a single gap to show, and ruin the look.

[Whiterabbit]

Finishing the sub box

Filler primer until it's an automotive quality finish



Chalkboard paint, then polish with 800 grit wet paper. The other secret to making it look like ABS. That, and using rounded corners on EVERYTHING.



Original, new.



Only thing left is to stuff the box (it's on the small size of what I want, but works), and install!





Obviously, waffle grilles are ugly, but if I hadn't documented the fact, you'd never know it was a $10 waffle grille after I put the grillecloth on.

Also note the false floor is upholstered on the bottom side with CCF. Not shown, but the bottom side of the subwoofer box is upholstered in CCF too. When I measured the 1/8" clearance, BOTH of these were taken into account, or else I'd be in trouble when I put it all together!



I lose 4 dB of volume with the floor down vs up. This is OK because this subwoofer can easily blow over all my speakers, so I can compensate without issue.

Two things not shown here.

#1, The grille bolts. I used, I think, 5/8-24" machine screws, 3/4" long. I used brads to stick the grille to the top of the box. Then I countersunk, drilled, and tapped the top of the box for the 4 very large bolts. I bought black chromate screws from fastenal so they colormatched. Then I used the filler primer and paint and sanded the box to perfection. THEN I use a flathead screwdriver to pry off the grille, clean up the edges, re-spray the brad holes, re-finish the box.

That way, when I screw the grille on, the sides line up perfect, right down to the thickness of the paint.

#2, the wiring. The wiring was cleaned up with cloth electrical tape. That's what Mercedes used for the OEM wiring behind the panels, so that's what I used. The ribbon of wiring across the top, today, is wrapped up in cloth electrical tape, identical to the OEM harnessing. Ditto forthe remote wire an any other wiring travelling elsewhere in the vehicle.

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Well, that's it. There are some other clever things I did but have no documentation for. A pigtail with the MS8 and 2x USB cables wrapped up in the side panel so I can tune from the drivers seat. the D-block. The piggyback ECU tied into the OEM harnessing so cleanly, no smog tech will be able to see that it is aftermarket. my cell phone holder with a wireless charger integrated so I don't need to use cable chargers in the car. Simple little "clever" things.

Anyways, I hope you enjoyed it. I've done crazier installs, I've done installs that earn more points in IASCA, but this one is simple and clean. It lets me tune in REW to my heart's content, play with FIR filters, run 2.1, 5.1, 7.1 (though the sides are midbass only, so that's stupid). Let's me play with midbass arrays. Let's me try 1-way, 2-way, 3-way center. Gives me a ton of bottom-end. Gets loud and boogies. And leaves me with a spare Be3 in case I blow the first one

Fun little car

[Ge0]

To damn tired tonight to comment. But subscribed. Looking good. Rock N Roll Wabbit .

Ge0

[BigAl205]

Are you going to do any custom steering wheel controls this time?

[LBaudio]

nice and clean,.... but most important... How does it sounds?

[Whiterabbit]

ah ha! I will totally build a crazy car again with all the bells and whistles I can think of, but if I do it'll be an older car where I'm "more free" to put on my creative hat and go hog wild.

How's it sound? Overall, the sound is excellent. Despite being 5.1, the car IS a 1-seat car. tuned for no-compromise in the driver's seat, so there is some right-side steering for the passenger. Inevitable.

The strategy is simple. Use the MS-8 to clean up the OEM amp to flat, and provide the basic tune. It is expected that this will properly set the time alignments too. After that, to use the miniDSP to fine tune and fix any measurement issues with the sound using a calibrated mic and REW. It also allows for experimentation with FIR which is a really neat feature. Basically, miniDSP for me is just a really fancy EQ.

The center channel is crisp and planted. It's 5.1, so lots of time was spent here aligning the response with my selected room curve. EVERYTHING follows from this, so it has to be right. The center is like a mono-car, dash level and with reasonable distance from the listening position.

The mains are tuned via miniDSP to match the center. Lots of time spent here too. The overall result is a handsome sounding car. There are fundamental design issues that can NEVER be compensated for in a build like this. The stage is never PERFECTLY distributed from far left to far right, there is still some compression between extreme sides and the center. But the DSP power I have gets me much farther than I could with a more traditional signal path setup. One surprise is the width of the car. The stage width leaves nothing to be desired.

That means the midbass array concept is a largely wasted concept. I've played with it, but it's either not needed, or I'm not tuning it right. Overall, it only muddies the waters. The truth is I have them at -15dB and they contribute basically nothing to the car. But I can turn them back on in a matter of minutes and tune again anytime I want. I have the mini DSP channels for it ready to go!

The rears are not post-tuneable. If I were going ground up, I would add another miniDSP and tune these also. However, it's really a waste of time and money to do so. The transparency to the stage is not 100% perfect since the stage has fine tuning and the rears do not. However, all I have to do is drop them 2-3 dB or so and I get the same effect. If they are not transparent, they just drop out and I get less room-effect with them. It's good enough because let's be honest, the surrounds are a fun gimmick to enjoy, not a critical part of the enjoyment.




Overall, zero complaints, and were I to go to competition, unless something has changed, I believe I'll easily be in the top 5 and possibly the top 3. I have a garage full of silver medals and 2nd place trophies, so I make no grand illusions about taking first here, we got some way, way good cars. Or at least we did 8 years ago when I was competing more regularly!