Robert, I understand what you’re saying. But honestly, “rattles my walls” is not a good indication of subwoofer performance. That speaks more to the quality of wall construction and possibly lack of decoupling between sub and floor. It could be any specific frequency between 20 and 120 Hz. or higher causing that rattle. This is no indication of how good your response is from 20-60 Hz. or even below 20 Hz. In other words, if it’s an 80 hz. frequency causing the rattle, that tells you nothing about how much output you are getting between 20-60 Hz., which is where a lot of important movie effects fall. Have you measured your actual frequency response in your room to know what kind of decibel levels you’re even getting between 20-60 Hz? How much distortion is introduced when you play it at reference levels?
It all comes down to what your expectations are. Home cinema “reference” level is generally considered to be 79 dB. Subs need 30 dB of headroom over that for peaks. So, ideally, your subs for home theater should be able to hit 109 dB peaks from at least 20-120 Hz., without introducing lots of distortion. Now most people probably don’t want to play it that loud, for reasons like the walls rattling, disturbing the neighbors, etc. As I said, it all comes down to expectations. But for the cost of the BF-210 compared to competitors, I would expect reference level performance. The bottom line is the BF-210 is really designed to pair well with ML’s for music, not for home theater. A small cabinet sealed sub is at an inherent disadvantage especially in the 20-40 Hz. range for home theater use. For the cost of a single BF-210, you could probably get a pair of ported subs from Rythmik or PSA that would perform much better for home theater.
The truth is, just about any sub sounds “good enough” until you hear a better performing sub in the same room. It’s hard to understand what you are missing until you experience the difference. That’s why measuring and calibrating are so important for subs. To understand how they are actually performing in the room. By the way, having your amp volume just under half probably means you’ve got just over 3 dB headroom. Remember, it takes double the amp power to raise the output by 3 dB. And that’s not a lot louder. That’s about the minimum amount of headroom you would want.