My new room caused my a lot a of problems in low end spectrum. I've changed postion of speakers, I've changed position of a desk, I even changed my speakers for a while. AVVA solved all my problems straight out of the box. I bought just one unit. I'm using also a regular Hofa bass trap in the corner. It's pure magic. As a mastering engineer I can say it brought my setup to a reference level (even though it's only my project studio). Quality is excellent, I would say even better that PSI speakers I've tested recently. I would give it a 6:)