This link provided by someone above is a problem with some of these tweeters problems (PSB this case) when not done right. A lot of people don't notice it, but others do, and the measurements show it's there. A young couple posted here about Paradigm speakers they bought and couldn't listen to, and were seeking answers to try and rectify their problem. They bought theirs on reviews and hoped they would work. It may be ultrasonic noise, but definitely cause irritations to a lot that are sensitive to it, like the couple I mentioned. I don't know why they make speakers that do what these do. PSB problem in the first, Paradigm problem in the second link. They also talk about congested midrange in the PSB. [http://www.stereophile.com/content/psb-image-b6-loudspeaker-measurements] [http://www.stereophile.com/content/paradigm-reference-studio-60-v5-loudspeaker-measurements]