You can get to the HK sub by snapping off the lid on top of the rear compartment. The lid is attached in four spots. The forward snaps will give way first. Just make sure to keep the lid flat and pull straight up.
The subwoofer is held in place by four screws. Be careful removing the screws because if you drop one it might be difficult to find. Once the screws are removed, you can unhook the wiring harness that attaches the HK sub (it’s tough to undo the first time).
Once the enclosure is removed, you can see how the process was designed to work. One speaker is facing forward and is ported out the front grill into the cabin. The rear speaker is not ported at all; it is wired in reverse phase and is solely designed to assist the front speaker (not to be heard on its own).
The HK sub has two speakers within the plastic box. The rear speaker (pictured on the right) is exposed. The wire plug (coming out of the left side) contains four wires, two for each speaker. (Click on any of the pictures for a larger view).
Looking inside the port hole you can see the second speaker. It is identical to the one on the back. Inside the cavity there is some stuffing. Playing around with the sound characteristic, I found that the sub sounds better at low volume with the stuffing removed, but it sounds much better at high volume with the stuffing. I say high volume, but truth is these are speakers that just can’t handle very much power. The HK sub is a really good sounding speaker up to a point, then everything starts to buzz and rattle.
Some stickers on the speakers claimed 2 ohms, but using an ohm meter, I tested each individual speaker at 3.4 ohms. It would be very interesting to try and find some really good aftermarket speakers that would fit in the same enclosure. I measured the speaker mounting points – it was 4 1/4 inches from the outside of one hole to another and 3 3/4 inches from the inside to inside (click on the picture to the right for a larger view). If anyone finds a possible replacement speaker that will fit, please tell me about it.
You can see there really isn’t much to this design. It’s a plastic molded speaker housing that has just enough room to contain the two speakers. Because of the compact design, there is not a lot of room for air to move. I think the tight design really leads to high air pressure, and the paper/cloth drivers perform up to a point but then the increased air pressure just restricts their movement and they start to distort. But all in all you have to really be impressed with the capabilities of such a small design. I think they could be improved upon, but not bad for stock speakers.