I know there are a handful of install posts related to adding an external sub to their X3...
Here's mine...
I chose the JL Audio micro 10 in a sealed enclosure due to the footprint.
The ported version probably would perform better, but I didn't want to give up those extra few inches in width and length.
@ 400 watts, it should perform better than any of the others I found in the market with similar size... Actually, no real competition regarding the size that I know of / this fits PERFECTLY between the latch rail and the side wall, so I can still open the trunk floor if/when I need/want to.
Self powered, so no additional amp to try to find real estate for...
and a bass control knob for personalized song-by-song performance.
https://www.crutchfield.com/S-YxxSG9...xoCIoMQAvD_BwE
https://www.crutchfield.com/S-AqSrTq...BoCGQQQAvD_BwE
Connections really could not be easier than in this car... Absolutely no reason anybody with extremely minor skills couldn't DIY this install.
NO SPLICES - - I used the TechnicPNP add-a-sub harness, which was plug and play at the amp behind the rear side panel, and used that with some rca cables to run the low pass signal to the amp/sub combo.
https://technicpnp.com/product/hifi-...ub-harnessloc/
Using an amp wiring kit from Kicker, 8ga fused hot wire and ground wire were a breeze.
HOT just bolted onto the battery at an access point.
GROUND just bolted onto the factory ground stud used by the battery.
https://www.amazon.com/Kicker-46PK8-...a-965633672357
The RCA cables routed along the side and across behind the rear seats.
The HOT cable routed across the other power cables to the opposite side, and tucked nicely under the floor rail.
The GROUND cable routed nicely under the rear floor.
and
The Bass Knob wire went across from behind the rear seats, alongside under the kick plates to the front floor boards, and EASILY tucked under the weatherstrip to enter beside and into the dashboard where I mounted it inside the headlight control unit / just under the fog light switch.
Actually, this was the most challenging part of the process - getting this to fit into that location.
Hard to see in the photos, but the enclosure is velcro'd both to the trunk flooring carpet, as well as the carpeted side wall for some stability. I may look into some kind of tether if I see this start to move around any, but I don't think it will.
Here are some pics: