SubWoofer Installation in an E28

The following was provided by Paul Craven.

I am using the factory amp plus a Rockford Fosgate Punch 45 watt amp for the sub (approx $100). The sub is a garden variety 8" Pioneer from Best Buy (maybe $60).I    do not have pictures or a digital camera, but the install is relatively straight forward. If you remove your back seat lower cushion this will all make sense, but there is a fairly large cavity on either side of the drive shaft hump. I put mine on the drivers side. Using 1/2 or 3/4 plywood, cut a plate to fit from the hump to the bulkhead. It needs to be close to an exact fit so take your time and test fit carefully. You will need a small vertical baffle across the back to seal it up and one across the front to drive screws through the bulkhead into. Cut a hole close to the hump for the speaker. Seal up all the factory openings in the bulkhead (unless you are using a free air sub) with cardboard and duct tape and run the wire for the speaker. Install the board using some sheet metal screws through the bulkhead and some into the floor. Then seal around the edges with duct tape. Put in the speaker and fire it up. You can get the input signal from the head unit or the factory amp OUTPUTS with a converter.

It's important seal the cavity/enclosure completely (since the woofer uses the trapped air as a damper) and to make sure the board is tightly secured to eliminate rattles. I know all the duct tape and cardboard sounds like a bad idea, but it's cheap (sorry, make that "low cost") and effective and you can only see it with the seat removed.

Click on one of the thumbnail images below to see the high-resolution picture: