Rating: - Boom Boom Rumble Boom
First, a bit of credentials, as this is my first review here.
I have many years of experience in good sound. Back in the day, I built and used Dynaco tube power amps from kits, and have owned Marantz, Mac and Crown amps as well. I had Tandberg cassette decks (anyone remember audio cassettes?), and Technics turntables. For speakers I've used Klipsch, JBL, Tannoy, Polk, Yamaha, and the insanely expensive - and worth every penny - Magneplanars from Magnepan. So, except for the Magnepan's, not quite audiophile, but really good home sound.

So, why would I buy a hundred dollar subwoofer from Amazon you ask?
I was looking for something inexpensive to give some bottom to the M-Audio powered speakers in my computer room, and I have seen and heard some new Polk speakers that sounded good, each in their respective price range.
Mostly, I bought this subwoofer based on the positive reviews on Amazon.

Sorry to say, I must disagree with the majority for this one.
I tried tuning it, I tried many different room placements, I tried various expensive subwoofer rca cables.
Sadly, I must report that I was unable to get any musical output from it - ever. I wasn't expecting audiophile here, just the ability to hear bass notes when they are playing. No-way, no-how.
I give it 2 stars for it's well made box, and the fact that it gives lots of rumble and (sloppy) boom, - and maybe that's enough for some.
But I have an almost 10 year old Yamaha sub (pre rca inputs, around the same power and same speaker size) that I brought into the room as an A/B test. The old Yamaha outperformed this new Polk by far.

After all of the positive reviews, I'm wondering if maybe the one I got was defective, but there is no way to get inside it for testing without voiding the return policy.
So...I returned it.
Good luck!