Gunbei--
Before you go out and spend money, experiment. Try sand and shot or just sand. Are the stands spiked to the floor and the speakers to the stand? And are they level? Other considerations are your speaker wires. What is in the rest of your system?
Before you go out and spend money, experiment. Try sand and shot or just sand. Are the stands spiked to the floor and the speakers to the stand? And are they level? Other considerations are your speaker wires. What is in the rest of your system?