I finally got around to finishing and hanging these after a year and a half of working on them on and off. The skyline diffusers are spec'd from the old BBC design many years back, and honestly they're more for aesthetics than functionality.
http://i.imgur.com/eehK8mt.jpghttp://i.imgur.com/oSphDv8.jpghttp://i.imgur.com/fdyb8ea.jpgEach set of diffusers consists of:
1 skyline diffuser made from aspen wood
1 skyline diffuser made from pine wood
1 skyline diffuser made from naturally grown heart redwood
1 skyline diffuser made from naturally grown douglas fir
The douglas fir and heart redwood are virtually impossible to get nowadays, but I was lucky enough to reappropriate some old lumber and run them through the planer.
Each diffuser is 12" by 12", consisting of 1" wells that are from 1.5" to 6" long. The width of the wood determines the high frequency effectiveness and the depth the low frequency effectiveness. These are effective from 500hz to 5000hz if my memory serves me correctly-- not that it really matters.
All-in-all, from the wood gathering, planing, cutting, gluing and hanging, I'd say this project took me around 60 hours to complete. Quite a bit longer than my diy basstraps in the corners of the room. I've seen so many people use stock-wood, but the planing process is perhaps the most important to making the diffusers look the best they can look.