Originally Posted by tojo_m
Any ideas how to add some good thump to the base audio system (US) in the F30?
Also does the stock system come with any frequency crossover system to pass just the lower frequencies to the two 8" subs (located below the seats) and the rest of the frequencies to the other speakers?
There are lots of options and ways to do what you want.
How experience are you with installing car audio?
Do you plan to do the install yourself, or pay to get it done?
Earthquake shallow mount subs are pretty good subs. I installed a pair in my 135i, just the subs nothing else. They improved the bass quality nicely. There was greater depth and cleaner output.
Maybe you should try just replacing the stock subs, replace the stock mids and tweets, add a 4 channel amp to drive all of it, and listen to how it sounds. It may give you all the bass you want, and you won't have to get another amp and sub in the trunk.
If I were doing it, I would get new front component mids/tweets, Earthquake subs, and amp.
Use the existing rear drivers and OEM amp, and add in the rear when you have passengers in the back.
By using just the front drivers with after market drivers and amp, it will give you a very nice sound stage, no reason to spend money on the rear drivers.