sub install idea for A4/S4
 

Just thought I would share a very effective sub design for the A4/S4. The design is based on a particle board based enclosure and a sealed box.

The sides of the sub box come flush with the rear seat back. The front of the box sits back about 2 inches from the seat back and has the same sloping angle parallel to the seat back. The box, as a whole, is centered over the ski sack opening. The sub itself is downfiring, but with about a 20 degree angle to the trunk floor aiming towards the front of the car such that the sound makes a primary reflection off the floor before being directed into the car through the ski-sack opening. The trunk panel of the ski-sack should be removed for best results. Really, the best results would be with the ski sack completely cut out, if one would so desire, but it works well enough with the sack still in place. The downward angle of the sub directed out through the ski sack creates very tight deep bass while eliminating boominess or "standing wave" type effect within the cabin that might have occurred if the driver was pointed directly into the cabin through the ski sack opening.

I'd do this if I had an A4
 

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Can't remember whose A4 this was. I like the general concept, though you could square-out the center for the ski sack. I'd mount the amp on the shelf, right-side-up.