Ever used perforated/slotted plasterboard?

Knauf produces plasterboards with pre-made holes (circular or rectangular) and slots. These are intended for sound absorption. Have any of you used boards like this? You don't have to build a plasterboard wall and then an absorber on top of it. It can serve as an absorbing wall. Check out (in German): Knauf Acoustic Ceiling Brochure http://www.knauf.de/bilder/katalog/3376 ... 10/D12.pdf

I've not tried this, but it seems like it could work. You would need to know the percentage of perforation to calculate the Hemholz frequency - If you did it right, this would sorta be an extension of John's "inside-out" walls... Steve