Can anyone tell me if the HK trunk subwoofer is a plug and play connection to the Alpine 9-speaker setup? I only ask because I have the opportunity to purchase the HK subwoofer cheap and wondering if it would work in my car. I believe the Alpine already has a small subwoofer "somewhere" but I'm thinking the HK trunk subwoofer might add a bit more oomph (is that a word?) to the sound.
If it matters, my car is a 2018 T/A 392 with the 9 speaker Alpine sound system.
AFAIK, the Alpine sound system options are 6 speaker (so just like the base audio setup but with higher quality speakers
) or 10 speaker (add'l center dash, rear deck sub, and rear seat sides
). If you have the 10 speaker Alpine setup, you should have an 8" free air sub woofer in the rear deck, in between the two 6.5" speakers. There is a hole there no matter what, but if the sound system didn't come with the 8" sub there, it's covered over by a piece of rubber/plastic to seal out the trunk air from the cabin air, or something like that.
As far as the HK subs being a plug and play for your system, I would say it is possible but not highly likely IMHO. Each of the optional subs will have wires present whether or not the subs are there from the factory, but the factory amp will not be putting power down those wires if it wasn't set up to at build-time. So if you use the rear-deck sub wires to power the HK sub you buy, it likely won't be getting any power from those wires and thus basically be inoperable. The same goes for if you use the factory wires for the HK subs, but your car didn't come with that sub. They won't be getting any power from the amp, so it will likely not work either.
Your idea is a sound one, but I do not believe the setup/configuration of the car's specific factory audio system will allow what you are wanting to do.
If I am incorrect in this, hopefully someone will come along and correct me...