They absolutely do work. I've installed six in my room, although I experimented with placement and ended up with a much different configuration than is suggested by the manufacturer (due, I think to the odd configuration of my listening room itself). Results - much smoother overall frequency response (got rid of a nasty 100 hz bump) and dramatically increased transparancy and air in the soundstage. The differences are not subbtle and others commenting are right on when they say removing them makes you realize how much you really need them. They also have to be one of, if not the most, cost effective improvements you can make in your system.