Speaker Placement. Hi there! I have a small problem about my speaker placement. I have Signet SL

Question

Hi there! I have a small problem about my speaker placement. I have Signet SL 260's and they utilyze the rear firing port for the bass. Now I live in a small appartment and it is not possible to place them the recommended 3 feet from the rear wall so I have them about a foot from the rear wall. The problem comes when I try to play music with heavy bass. The whole rear wall starts resonating and the people living upstairs complain about ``shaking'' appliances. The appartment complex that I live in has issued notices of possible fines of $200 for making loud noise. I would be gratefull if someone out there would be kind enough to suggest a possible solution for the resonating wall. (Yes I like to listen to music slightly loud) Thanx Saad