So my 2008 STI came with the OEM subwoofer installed under the driver seat, and at first I really hated it. After listening a bit more I've discovered that it actually does pretty well, it just has wayyyyy too much mid-bass and it makes it sound bad.

Anyway, I think if there were a way to install a lowpass filter on it, it could be made to sound good. Has anyone toyed around with this?

Also I'm planning on installing an aftermarket nav deck, which would of course have a built in subwoofer lowpass filter, but only on the RCA outputs. So my question is this....does the factory sub take a speaker (high) level input from the deck, or is there some sort of line (low) level signal being sent from the deck to the sub. If it's line level, I may be able to use the RCA subwoofer output on the aftermarket deck to drive it.

 

Assuming the 08 is similar to the previous years, the sub is speaker-level only and taps the rear speaker outputs of the HU. There should be gain and frequency adjustments on it, you may have to get in there with a flashlight to see them as the controls (at least on the older ones) are recessed into holes on the side. A small screwdriver is needed to adjust them.
Since it is speaker-level and not line-level, adding a crossover is not practical. Also there is only so much you can do with a small driver (it's 5" IIRC), you aren't going to get the low frequency response and definition you'd get with a larger sub.

 

I'm planning on getting one for my 2009 WRX and I'm studying as much as I can because, as jimmyz indicated, these systems tend to enfasize on mid freqs.

Although you can't use a normal crossover unit, you'd certainly be able to use line-level in-line filters. A low pass of your choosing would do the job; Crutchfield and others sell this.

Now, what I'm not sure about is if the HU does a crossover work, because I've read the HU needs to reset something before activating the sub.

 

stated this in a diff. thread but it is a POS...better than nothing but not worth what you'll pay for it.

Well unless you put it under the driver seat and like to have your choade tickled

 

What's a POS?

Some people say the Subaru's sub isn't as good as...say, Kenwood's. This is important because Subaru's is kind of expensive and for the same price a Kenwood or Jensen or other might be a better performer.

What's your say on this?