Over the years, I have used a varity of ferrite blockers/stoppers on power cords as well as interconnects. In my applications, they absolutely provided positive changes in that the noise floor was reduced. In using them however I had to "tune" the blocker/stopper to the best location on the cord/interconnect - to close to the source or to far away from the source resulted in too much or bloated bass or the sound suffered from compression. Once in the right spot on the cord/interconnect, they proved to be a most beneficial and economical tweak.