A quick story some of you may find interesting.
I was in a work friends new HT last night. He asked me over to try and figure out why his movie explosions sounded like... and I quote, "elephant farts."
His 5.1 system, installed by a supposed pro, consisted of 3 Polk in-wall front speakers and two Yamaha in-ceiling speakers behind his couch. On alternate side walls near the front were two of what I'm pretty sure were these, OEM Systems Stud Woofer
Luckily, I know this guy is rarely on the web and even less likely to ever view this board, so I feel safe in saying that this was absolutely the worst HT system, I ever heard. At least until you turned the subs off. Then it wasn't so bad.
The fronts sounded OK. Not astounding but not all that bad. Definitely an worthwhile improvement over his TV speakers. I hate ceiling speakers so I found the misplaced, side surrounds very distracting more than anything. Finally though, he sure wasn't kidding about the bass. I think "elephant farts" was exactly right on the money.
The speakers seemed secure but I couldn't get the covers off for some reason. The wall itself did not appear to be vibrating. We tried pressing against various parts of the surrounding drywall to see if we could reduce the ill effect but it didn't seem to change anything. Besides, you could actually tell the offending 'noise' came directly from the subs. Actually, the fact that the subs were easily identifiable by ear as the source of the 'noise' showed it wasn't producing true LFE anyways or it shouldn't be so easily isolated. They sounded, well... broken. But two of them the same?
We did improve it some.
I turned down the sub level a good bit in his receiver and it helped as it was working way too hard compared to the volume of everything else. I experimented with the crossover and we decided it sounded best (but still not good) with it set at 120. Sadly,what it was producing in place of the low end of LFE still sounded more like a giant whoopie cushion than resembling natural sound though.
He asked me what he could do and my advice was to challenge the so called "pro" on what was obviously not even an OK piece of an otherwise 'just OK' system. Either both subs suffering from some blown driver materials or some other defect or they were just a very, very poor choice of gear. Although, I did put it a bit more tactfully than that first part.
I suggested floor subs or at least demand an in-wall model that a.) are not broken or b.)does what it should by producing LFE, not farts. Otherwise his system sounded much better with the sub channel turned off than on, so therefore they were just a waste of money and better off removed and money refunded.
A fun evening of experimentation though, even if we couldn't fix things.