Those are nice mixmkr.
 
And then there are these for even more artistic acceptability.
 

...wicked
What I wanna know is the type of knauf insulation he used, the link in the blog post is dead. His pricing is blowing my mind!

How I built my bass traps...     1252 posts and counting.
 
If that isn't enough, then everything you could possibly want to know about this kind of stuff can be found at bass-traps-acoustic-panels-foam-etc
 
And for the rest of your studio : studio-building-acoustics

PopStarWannabe
 
"Would I do anything wrong if I filled the corner traps with sheep wool instead of Rockwool ?"

Everything is relative :-)
 
Here is a master chart of the absorption coefficients of a whole bunch of different types of insulation.  I think you'll be interested in "Second Nature's Thermafleece (Sheep)" down near the bottom.
 
From the chart you can see that different frequencies are absorbed differently, and the thicker your panel, the more that's absorbed.
 
I wouldn't use filled-corner traps on an outside corner of a house in an area that has cold winters.  You'll end up with condensation on the walls behind the insulation.  A flat panel across a corner should be fine and will increase the absorption of the panel.
 
Acoustic treatment is a tricky business.  You need lots of deep traps for low frequencies, dispersion for the high frequencies and a mix of both for the middle.  A small room will make all the usual problems worse.