Subwoofer upgrades questions for 128i

[GabeMG]

Hi everyone, I want to add a subwoofer to my 2011 non i-drive 128i, and haven't found much info on the actual installation process.

I'll break this post into two categories:

a) aftermarket subwoofer in trunk:
The typical sub install. I lean towards this because I want a speaker around the 500-800 watt rms range, and those are pretty common in the 10-12" size. I don't mind loosing trunk space, I never use it anyways.
My questions about this is mainly -- how to tap into the factory headunit for a speaker input? Would it be smart to tap into the existing under seat sub wiring?

b) Under seat sub upgrade:
This seems to be what I find the most about on this forum, however I don't really see anyone talking about the upgrade process much.
I know some companies make plug and play upgrades, but those tend to be pretty pricey.
Could I order any 8" shallow mount and drop it in? What about amps?

Hopefully this can turn into the guide for anyone looking to do this upgrade. Thanks!

[tracer bullet]

My HK system already had the reasonably decent 8" under the seats. Amplifying them w/ more power than stock helped a lot by itself. Adding a 10" in the trunk topped it off. I'd consider both if possible.

[GabeMG]

Originally Posted by tracer bullet

My HK system already had the reasonably decent 8" under the seats. Amplifying them w/ more power than stock helped a lot by itself. Adding a 10" in the trunk topped it off. I'd consider both if possible.

Tell me more about the upgrade process! Mine also has a decent sub under the seat, but I want a little more thump.

How'd you install the trunk sub? Any videos for install?

[tracer bullet]

MusicarNW was the shop that sold everything, I did the install. I think if you search around you'll find more about them.

It's a JL amp installed in the left rear of the trunk. 4 channels, 1 for each 8" and the other 2 bridged for the sub. Power and ground run over near the battery, the rest of the wiring via a custom connector adapter they made. Intercepts the signals to the 8".

https://musicarcertified.com/product...ass-level-one/

https://www.1addicts.com/forums/showthread.php?t=790113