I do not know what to say clearly about them. The construction and the materials are good. Inside I do not know if it is filled with rock wool or not. As a principle the 50hz tuning applies only to largest dimension depth that applies only to face to back corner...then an almost nothing as surface...being triangle. It seems to affect a little much upper freq. In my small room with 2 of them placed in front at half distance between speakers and the wall next to them...not fully in corners because in left I have a door...the effect measured in rew in any way it is minimal to totally absent. Maybe with 8 of them you will achieve some measurable effect but then the cost will be very big. As placebo almost I like to think that it clarifies the sound just a tad...but at 280€ for 2 pieces is hard for me to recommend them.