Audi A3 – Custom Stealth Audio System Install

The goal of this install was to have a clean install with that maintained that stock look. I decided to that I wanted to keep my steering wheel track and volume controls so I opt to stick with the factory Concert II head unit. I wasn’t impressed by the factory subwoofer so I decided to remove it and build a custom fiberglass stealth sub enclosure. I wanted to keep my cargo area available and not have a clunky speaker box to contend with.

Components Used:

Head Unit: Stock Concert II

Amplifier 1: Alpine PDX 4.150

Amplifier 2: Stock Amplifier

Subwoofer: JL 10W3 v3

Power Wire: 4 Guage

Front Seperates: Focal 165 v2 6 1/2″ Components

Rear Seperates: Stock

Interconnect: Monster Cable Interlink 400 MkII 4m

CD Changer: AUDI USB/MP3 Interface Model V (Xcarlink)

Lineout Converter: 2 Channel lineout converter

Head Unit

The Facotry system is composed of a Concert II (Non Bose) head unit. The biggest problem with the Concert II is that there are no RCA outputs to supply the signal to the aftermarket amplifier. I used a simple line-out converter to solve this problem. I was very hesitant with this solution as it could introduce noise or produce a dirty signal to the amplifier. After fine tuning the gains on the LOC, I was able to produce a clean signal to the amplifier.

Stock Wiring DiagramStock Wiring Diagram 

 

New Wiring Diagram

Speakers

 Although the stock seperates were decent, the 4″ Factory Boot Sub was less than par. I decided to keep the stock rear speakers to be used for rear fill and to upgrade the front speakers to Focal 165-v2. The Focals to me had a smooth mid range and smooth crisp highs. Normal power handling is 75 Watts RMS  with a Peak of 150 Watts with a mounting depth of 2.83″.  The Cross over provided is a 2-way 12dB/octave (with adjustable tweeter level).

For the Subwoofer, I chose to run JL Audio 10W3v3-4. The speaker only requires 1.14 cubic feet and the mounting depth is perfect for a smaller stealth enclosure. The sub is rated at 300Watt RMS at 4 ohms.

Amplifier

I chose the Alpine PDX 4.150 digital amplifier for its Ultra Efficient, Ultra Powerful, and Ultra Small form factor.  This 4 channel amp has plenty of power to give with a 150 Watt RMS per channel. It handles both 2-Ohm and 4-Ohm loads with the same power handling, or 300 Watts RMS Bridged x2. Let me tell you, with this amp, size does not matter. This is a Class-D amp in a sub compact frame. Clean crisp power running at lower temperatures than a analog amp.

  • 4-channel car amplifier
  • 150 watts RMS x 4 at 4 ohms (150 watts RMS x 4 at 2 ohms)
  • 300 watts RMS x 2 in bridged mode (4-ohm stable in bridged mode)
  • variable high- and low-pass filters (30-400 Hz, 12 dB/octave)
  • Class-D amplifier design
  • stackable installation design with front-panel controls
  • quick-connect speaker connectors
  • preamp-level inputs
  • MOSFET power and output stages
  • CEA-2006 compliant
  • 10-3/16″W x 2-1/2″H x 8-7/8″L
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    The Install

    I started the install by dissecting the car. Removed the door panels, bottom dash covering, glove box, both kick panels, both side door sill, backseat, and everything in the trunk. The front door speakers had to be removed. The stock speaker boot could not be removed since its actually glued to the speaker so I had to fabricate my own speaker rings. I made a couple MDF speaker rings and put foam on the back side of it and mounted it to do the door panels. The MDF rings when attached to the door made for a solid foundation for the speakers to kick. The stock speaker wires are worthless so I replace it with heavier gauge silicone insulated speaker wire. Getting through the rubber grommet on the door was a difficult however it just had to be done.

     

    The tweeters were a little difficult to get in and out of the A-pillar. The plastic is very fragile and took careful maneuvering to remove it. The Focals did not fit in the stock mounting bracket. I ended up gluing the focal tweeters to the plastic speaker grill. I’ll need to figure out a better way to do this later. I was thinking about making fiberglass speaker pods but thats another project down the road.

     

    I ran the power wire through the engine compartment firewall through a  grommet found under driver side dash. You’ll have to remove the rubber floor insulation to find the gromet. I used a 4 gauge power cable to supply power the Alpine PDX 4.150.

     

    Here are more pics of the wiring behind the glove box. To get the large power wire to the amp which is located in the trunk of the car, I had to dremel out a hole in the back seat frame.

     

    The 4″ factory sub was removed. The factory amp is found inside of the of the sub enclosure. This amp powers both the sub and rear door speakers. I removed the amp from the factory sub and built a case for it using a plastic Project box found at Radio Shack. I will be using this amp in the final  install to power the rear stock speakers just for rear fills, nothing fancy.   

     

    The new Stealth Enclosure will house a 10″ JL 10w3 which means it will be a lot deeper than the factory sub boot. In order to accommodate the depth of the new enclosure I cut out a metal panel in the left side trunk where the factory sub was previously. Behind the cut out is a large cavity however the new fiberglass steathbox will need to have a contoured fit to be able to slide in and out of the slot that was cut out for it. I taped of the area and filled the rear cavity with expanding foam. After the foam hardened, I shaped it using a knife to the mold of rear of the fiberglass enclosure. After shaping it, I added more tape to cover the foam. Now that the mold is ready, I started the fiber glassing. NOTE: DONT FORGET TO PUT MOLD RELEASE BEFORE YOU START FIBERGLASSING!! I FORGOT AND HAD A HELL OF A TIME removing the hardened rear shell. For the fiberglass work, I used heaviest fiberglass chopped strand mat that I could find and laminated with marine resin. Layer after layer of fiberglass was applied until I had a thickness of about a 1/4″. 

     

    After removing the rear shell from the car, I continued to apply more glass to the inside of the box until I built up the thickness to about 1/2″. For this step, I used a mat that consisted of half weave and half chopped strands.  Now came the “fun part” of trimming the fiberglass with a grinder and cut off wheel. The full body tyvek bunny suit I purchased was money well spent! 

     

    After the glasswork was complete, I fabricated an MDF Speaker ring to accommodate the 10″ woofer as well as a mounting bracket for the enclosures speaker connectors. Did more glassing to lock the speaker ring in place. After the ring was glassed in place, I started on the front of the enclosure. Started by stretching black fleece over the front of the enclosure. Applied several coats of resin and continued with the glasswork to build up the front thickness of the enclosure. **For the final coat of resin, I used finishing resin and coated the entire enclosure inside and out. The finishing resin dries hard and allows for easier sanding as well as to trap any smell that the tacky laminating marine resin was emitting.

     

    More fun grinding fiberglass and sanding! Don’t forget to wear a good quality respirator filter and goggles. A little bit of Bondo auto body filler was added to smooth the face and a whole lot more sanding gradually working it to a wet sand finish. Sprayed several coats of Primer, wet sand till smooth and then sprayed several coats of color enamel. Applied a clear coated it to finish it all off.

     

     After removing the tape and expanding foam from the trunk area, I added cushion foam to fill the cavities and applied Dynomat to the body panels in the surrounding area. I should have applied the dynomat prior to the initial mold/glass work but what the hell, it still works and everything still fit. 

     

    Here’s a pick of the finished stealth sub enclosure with the factory amp mounted in a surround of cushion foam in an empty cavity next to stealth sub enclosure.

     

    Built an amplifier rack out of MDF complete with AUDI Styling rings. The Audi rings made for a good heat vent! :)   Finished off the amp rack with some matching charcoal carpet. The rack is actually recessed into the foam trunk lining for that stock look. It can be easily removed for access to the spare tire beneath it. The stock trunk floor panel fits right over this for a flush stock look. Only when you lift the trunk floor panel will you see the amp rack.

     

    I wanted to complete the stealth box enclosure with a carbon fiber Audi Emblem Bezel used as a functional speaker grill.  I laminated carbon fiber over a thin piece of MDF until I got the thickness I desired. Added a final coat of epoxy resin for the deep gloss look. After everything hardened and cured, I drew on my template and Rotozipped the Audi Rings.

     

    I applied several layers of fiberglass to the inside of the rear panel that the stealth enclosure would sit behind to strengthen and reduce possible vibrations from the hard hitting sub inches behind it. Rotozipped the cut out for the speaker grill and mounted the carbon fiber bezel with a metal mesh behind it.

     

    Added a couple strips of RED LED’s behind the panel to illuminate the speaker just for show. :)

     

    Enjoy!

    Please leave a comment or advice for others