Hey guys,
I have finished today my subwoofer retrofit and would like to share some pics and details with you.
My GC is originally equipped with the Bang&Olufsen and although this system not sounding that bad, some more bass foundation wouldn´t hurt
I made a first try, using a free air subwoofer (infinite baffle principle), since I wanted to prevent building a box for the chassis. This attempt was not bad, but since trunk volume was too big for the chassis, it sometimes does not play precise.
Therefore I bought another chassis and build a sealed box, which is located right behind ski bag opening.
But lets start with the used equipment:
Amplifier is a Focal Solid 1 ... a small analogue Monoblock, which I use already for years in several BMW´s, because it doesn´t disturb radio reception. It delivers 300 watts rms @ 4 ohms and 470 watts @ 2 ohms.
The chassis is an ARC Audio "ARC 12D4v3" .. double voice coil with 4 ohms each.
Connecting the amp:
Since signal transmission from headunit to origin B&O amplifier is via bus system, therefore I had to tap the signal for my Focal amp at the speaker wiring from B&O amp to under-seat woofers. These cables can e.g. found underneath rear bench.
The origin under-seat woofers still operate as usual .. the parallel connected cables are attached to high level input of amp.
The amp itself sits on a plate, attached to rear seat backrest. I made grooves on the bottom side of plate in order to hide the wiring.
Power for amp comes directly from battery, certainly with its own fuse. Grounding from central grounding point in trunk. The 12 volts turn on power for amp is tapped from wiring harness of park break control device.
Subwoofer box:
I decided to build a sealed box, since they use to play precise. The ARC 12 chassis plays well in 30 - 40 liters box volume ... my box finally became around 37 liters.
The box is build of solid birch multiplex wood, which is stable and comparably lightweight.
Since I have attached the amp to the backrest, it was necessary to adapt the shape of box accordingly.
Here some pics of the box - I have painted the box with black acrylic paint for protecting from moisture.
Here some pics of box in trunk from front side .. you can also see the amp and the cut out area for the amp at the box.
I made the frame around chassis in order to seal box / backrest gap.
Btw., reason I chose this position for amp is the perfect accessibility.
Here the view from trunk side ..
I certainly made a cover in trunk and this it how it finally looks like ... as you will see, you see nothing - exactly what I wanted.
And finally the view from front ..
It really sounds much better than before ... now the chassis is still changing performance during run in phase, but it already performs quite good - I like it