As the subject of my post indicates, I'm a complete noob to HT construction, so please be gentle. I live in a semi-detached house, which means I share a wall with my next-door neighbor. I have my HT set up in my basement, front of the HT along the shared wall, no other choice given the arrangement of my basement. I was recently testing out my 2 subs (HSU STF-2 and Dayton 10") with one in the left corner and the other in the right corner. Given this set up, both the subs have their ports firing into the shared wall. After about 10 minutes of extreme non-stop bass, my doorbell rang and low and behold it was my neighbor. She politely asked me to turn down my subwoofer because her entire main floor was shaking. Although I had a rather large grin on my face due to the satisfaction that my subs are that powerful, I felt bad and immediately moved my Dayton 10" out of the front corner and into the back wall, behind my couches. So, last night I was watching Blade 2 at about 8 dB below ref level on my AVR's dial, with the HSU in the front firing into the shared wall and the Dayton in the back behind my couch, and my doorbell rang again. It was my neighbor's husband this time and he told me that he "doesn't wanna sound like a complainer" but he has a glass table on his main floor that is rattling like a bitch. I was rather inclined to tell him to put some felt padding to make that table stop rattling, but instead I apologized and continued watching the movie at a lower volume This really sucks because it basically means I can't watch movies at my preferred listening level without having my neighbor ring my doorbell! Either he is being too "anal" about it all or my sub is really shaking his walls beyond acceptable levels. I thought I had initially solved the problem by moving one of the subs completely away from the shared wall, but it seems the HSU is still too overpowering. I've moved the HSU away from the wall by another foot, so now it's about 3-4 feet from the shared wall, which I think still won't solve anything. Unfortunately, these houses were built 4 years ago, so there's absolutely no concrete in the walls between the 2 houses. I have about 4-6 inches I can work with on my shared wall in the basement. What can I do to the wall to stop or dampen the sub's waves from flowing through and causing my neighbor's walls to shake? Short of breaking the wall and filling it with concrete, is there anything that can be done, preferably rather inexpensively? Even if I do insulate that wall, won't the sub's frequencies still flow through my basement's ceiling to my main floor and consequently to my neighbor's main floor? I would really like to enjoy my HT/sub at high volumes once in a while: is there any hope? Moving to a detached house is not an option ... maybe in 5 years, but not now.